Just sharing my list of other Discourse sites I am aware.
This is a Wiki so anyone with a high enough trust level can edit it or add to it.
http://discourse.col.org/
http://discourse.cs3110.org/
http://discourse.solusiti.com/login
http://forum.writethedocs.org/
http://forums.valvoline.com/
http://forums.xgenstudios.com/
https://agopengps.discourse.group/
https://angular-japan.discourse.group/
https://app-meta.cdck-prod-meta.discourse.cloud/
https://beteiligungsplattform1.iwvi.uni-koblenz.de/login
https://cdnjs.discourse.group/
https://chat.aero.edu.au/
https://cidian.social/
https://cinelartv.discourse.group/
https://community.airgarden.com.au/
https://community.anker.com/
https://community.anovaculinary.com/
https://community.atlasobscura.com/
https://community.badvoltage.org/
https://community.balloonchallenge.org/
https://community.baserow.io/
https://community.bitnami.com/
https://community.bitwarden.com/
https://community.bnz.co.nz/
https://community.brave.com/
https://community.cartalk.com/
https://community.checkpoint.com/
https://community.cloudflare.com/
https://community.codecov.com/
https://community.codecov.io/
https://community.confessionsofahomeschooler.com/
https://community.containo.us/
https://community.databricks.com/s/
https://community.dataquest.io/
https://community.datastax.com/
https://community.dbdiagram.io/
https://community.developer.atlassian.com/
https://community.diem.com/
https://community.drownedinsound.com/
https://community.dsf.ninja/
https://community.endlessos.com/
https://community.endnote.com/
https://community.fatbesties.ca/login
https://community.gamedev.tv/
https://community.gemsofwar.com/
https://community.glowforge.com/
https://community.grafana.com/
https://community.home-assistant.io/
https://community.hubitat.com/
https://community.humanetech.com/
https://community.icons8.com/
https://community.ido-data.fr/login
https://community.ifit.com/login
https://community.imperia.de/login
https://community.incuto.com/login
https://community.infiniteflight.com/
https://community.influxdata.com/
https://community.info-beamer.com/
https://community.jitsi.org/
https://community.kodekloud.com/
https://community.kodular.io/
https://community.letsencrypt.org/
https://community.memrise.com/
https://community.metabrainz.org/
https://community.morphmarket.com/
https://community.mp3tag.de/
https://community.mycroft.ai/
https://community.mydevices.com/
https://community.mypaint.org/
https://community.n8n.io/
https://community.naturephotographers.network/
https://community.neo4j.com/
https://community.nulab.com/
https://community.octoprint.org/
https://community.openai.com/
https://community.openhab.org/
https://community.pagerduty.com/forum/
https://community.parseplatform.org/
https://community.pinecone.io/
https://community.postcrossing.com/
https://community.quickfile.co.uk/
https://community.raspberryshake.org/
https://community.render.com/
https://community.replicated.com/
https://community.revolut.com/
https://community.roonlabs.com/
https://community.rstudio.com/
https://community.sccm.org/
https://community.skrill.com/
https://community.smartthings.com/
https://community.sonarsource.com/
https://community.sphero.com/
https://community.stackedit.io/
https://community.swiftype.com/
https://community.tillerhq.com/
https://community.unbounce.com/
https://communityforum.appen.com/login
https://comunidade.nubank.com.br/
https://comunidade.tecnoblog.net/categories
https://connectdev.discourse.group/
https://contributors.scala-lang.org/
https://coq.discourse.group/
https://coronasafe.discourse.group/
https://crucible.hubbe.net/
https://cubebrush.co/
https://cwl.discourse.group/
https://cylc.discourse.group/
https://dartsim.discourse.group/
https://dat.discourse.group/
https://datalore-forum.jetbrains.com/
https://datashield.discourse.group/
https://developer.mypurecloud.com/forum/
https://developer.sailpoint.com/discuss/
https://devforum.roblox.com/
https://devforum.zoom.us/
https://devilbox.discourse.group/
https://discourse.acados.org/
https://discourse.acra.io/login
https://discourse.aicrowd.com/
https://discourse.algolia.com/
https://discourse.allennlp.org/
https://discourse.appimage.org/
https://discourse.ardour.org/
https://discourse.bigdaddylinux.com/
https://discourse.bigdinosaur.org/
https://discourse.biologos.org/
https://discourse.bokeh.org/
https://discourse.bootstrapworld.org/login
https://discourse.brew.sh/
https://discourse.cakephp.org/
https://discourse.cataclysmdda.org/
https://discourse.chef.io/
https://discourse.cmake.org/
https://discourse.codecombat.com/
https://discourse.codinghorror.com/
https://discourse.coreelec.org/
https://discourse.danielsousa.io/
https://discourse.datamethods.org/
https://discourse.mcneel.com/
https://discourse.destinationlinux.network/
https://discourse.digitalhealth.net/
https://discourse.elm-lang.org/
https://discourse.flathub.org/
https://discourse.gbif.org/
https://discourse.getdbt.com/
https://discourse.getgrav.org/
https://discourse.gnome.org/
https://discourse.gohugo.io/
https://discourse.haproxy.org/
https://discourse.haskell.org/
https://discourse.hibernate.org/
https://discourse.holoviz.org/
https://discourse.huel.com/
https://discourse.iagotechnologie.fr/login
https://discourse.igniterealtime.org/
https://discourse.imangistudios.com/login
https://discourse.ioquake.org/
https://discourse.irem.org/login
https://discourse.itk.org/
https://discourse.jabref.org/
https://discourse.joinmastodon.org/
https://discourse.joplinapp.org/
https://discourse.juju.is/
https://discourse.julialang.org/
https://discourse.jupyter.org/
https://discourse.kuvacode.com/
https://discourse.libcinder.org/
https://discourse.libsdl.org/
https://discourse.linuxserver.io/
https://discourse.littlebird.com.au/
https://discourse.looker.com/
https://discourse.matplotlib.org/
https://discourse.mapeditor.org/
https://discourse.mc-stan.org/
https://discourse.mcneel.com/
https://discourse.mitmproxy.org/
https://discourse.mopidy.com/
https://discourse.mozilla.org/
https://discourse.myriadrf.org/
https://discourse.nixos.org/
https://discourse.nodered.org/
https://discourse.numenta.org/
https://discourse.ohie.org/
https://discourse.omnigroup.com/
https://discourse.openehr.org/
https://discourse.opengenus.org/
https://discourse.openpnp.org/
https://discourse.opentechschool.org/
https://discourse.osmc.tv/
https://discourse.panda3d.org/
https://discourse.paraview.org/
https://discourse.peacefulscience.org/
https://discourse.pi-hole.net/
https://discourse.pi64.win/
https://discourse.processing.org/
https://discourse.prongs.org/
https://discourse.psychopy.org/
https://discourse.purescript.org/
https://discourse.radiance-online.org/
https://discourse.roots.io/
https://discourse.ros.org/
https://discourse.rspeer.org/
https://discourse.savta.org/login
https://discourse.saylor.org/
https://discourse.shadowsocks.org/
https://discourse.shapr3d.com/
https://discourse.skcript.com/
https://discourse.slicer.org/
https://discourse.slotcartalk.com/login
https://discourse.snowplowanalytics.com/
https://discourse.southlondonmakerspace.org/
https://discourse.soylent.com/
https://discourse.stimulusjs.org/
https://discourse.suttacentral.net/
https://discourse.threejs.org/
https://discourse.ubuntu.com/
https://discourse.ubuntubudgie.org/
https://discourse.ubuntudde.com/
https://discourse.videolan.org
https://discourse.vvvv.org/
https://discourse.web.cern.ch/
https://discourse.webflow.com/
https://discourse.zynthian.org/
https://discuss.3dprintingcanada.com/login
https://discuss.aerospike.com/
https://discuss.analyticsvidhya.com/
https://discuss.ardupilot.org/
https://discuss.atom.io/
https://discuss.circleci.com/
https://discuss.codecademy.com/
https://discuss.dgraph.io/
https://discuss.dvc.org/
https://discuss.educative.io/
https://discuss.elastic.co/
https://discuss.emberjs.com/
https://discuss.erpnext.com/
https://discuss.flynumber.com/
https://discuss.foss4lib.org/
https://discuss.huel.com/
https://discuss.iatistandard.org/
https://discuss.iccsafe.org/
https://discuss.ideasforsocial.org/
https://discuss.ii.coop/
https://discuss.inventables.com/
https://discuss.ipfs.tech/
https://discuss.kotlinlang.org/
https://discuss.kubernetes.io/
https://discuss.linodians.com/
https://discuss.linuxcontainers.org/
https://discuss.machinerypete.com/
https://discuss.newrelic.com/
https://discuss.ocaml.org/
https://discuss.pixls.us/
https://discuss.prosemirror.net/
https://discuss.python.org/
https://discuss.pytorch.org/
https://discuss.rubyonrails.org/
https://discuss.studiofow.com/
https://discuss.terminusdb.com/
https://discussion.dreamhost.com/
https://discussion.fedoraproject.org/
https://discussion.informationisbeautiful.net
https://discussion.informationisbeautiful.net/login
https://discussion.squadhelp.com
https://discussions.flightaware.com/
https://diyhue.discourse.group/
https://donkey.discourse.group/
https://duforum.in/
https://dust3d.discourse.group/
https://dvs.discourse.group/
https://edgex.discourse.group/
https://eldraeverse.discourse.group/
https://eleceasy.com/
https://elife.discourse.group/login
https://elixirforum.com/
https://es.discourse.group/
https://eshipdiscussion.lyle.smu.edu/
https://eve.community/
https://experts.feverbee.com/
https://fairfoodforum.org.au/
https://faq.inetsoftware.de/
https://faq.intrinsyc.com/
https://feedback.dxo.com/
https://fenicsproject.discourse.group/
https://foro.estudiabetes.org/
https://fortran-lang.discourse.group/
https://forum-db.informatik.uni-tuebingen.de/login
https://forum.1net.org/
https://forum.3dkoenig.de/
https://forum.3rails.fr/
https://forum.3tcsoftware.com/login
https://forum.absia.asn.au/login
https://forum.acolab.fr/
https://forum.akaipro.com/login
https://forum.am22tech.com/
https://forum.arduino.cc/
https://forum.asana.com/
https://forum.audacityteam.org/
https://forum.auto.revidian.com/
https://forum.banana-pi.org/
https://forum.bonsaimirai.com/
https://forum.cockroachlabs.com/
https://forum.cohesion3d.com/
https://forum.collaboraonline.com/
https://forum.core-electronics.com.au/
https://forum.dapphero.io/
https://forum.data2viz.io/
https://forum.datalore.io/
https://forum.dataschool.io/login
https://forum.dbpedia.org/
https://forum.devsource.xyz/
https://forum.dexterindustries.com/
https://forum.dobot.cc/
https://forum.downtomeet.com/
https://forum.duelistsunite.org/
https://forum.f-droid.org/
https://forum.facepunch.com/
https://forum.factset.com/
https://forum.fairphone.com/
https://forum.faithcsde.com/
https://forum.figma.com/
https://forum.flowster.app/
https://forum.fractalfuture.net/
https://forum.freeton.org/
https://forum.gethopscotch.com/
https://forum.gitlab.com/
https://forum.glamour.de/
https://forum.golangbridge.org/
https://forum.graphviz.org/
https://forum.grid.space/
https://forum.hamburg-tourism.de/login
https://forum.hellboundbloggers.com/
https://forum.iceni.com/
https://forum.idevfun.io/
https://forum.ignitioncasino.eu/
https://forum.igvault.com/login
https://forum.inaturalist.org/
https://forum.informedplanet.org/login
https://forum.ionicframework.com/
https://forum.juce.com/
https://forum.kicad.info/
https://forum.kingdomcomerpg.com/
https://forum.laravel-livewire.com/
https://forum.lesnumeriques.com/
https://forum.level1techs.com/
https://forum.lightburnsoftware.com/
https://forum.ludia.com/
https://forum.makehackvoid.com/
https://forum.makerforums.info/
https://forum.mangoh.io/
https://forum.manjaro.org/
https://forum.manycam.com/
https://forum.mattermost.org/
https://forum.mautic.org/
https://forum.mcarbo.com/
https://forum.melbpc.org.au/login
https://forum.metasfresh.org/
https://forum.monocycle.info/
https://forum.mssociety.org.uk/
https://forum.mutable-instruments.net/
https://forum.mysubscriptionaddiction.com/
https://forum.obsidian.md/
https://forum.okfn.de/
https://forum.opencv.org/
https://forum.openmandriva.org/
https://forum.opennebula.io/
https://forum.openwrt.org/
https://forum.pinegrow.com/
https://forum.pkp.sfu.ca/
https://forum.plentymarkets.com/login
https://forum.pokemongohub.net/
https://forum.projecthax.com/
https://forum.qpay.uz/
https://forum.restic.net/
https://forum.sailboatdata.com/
https://forum.savingforcollege.com/
https://forum.saysomethingin.com
https://forum.schizophrenia.com/
https://forum.seeedstudio.com/
https://forum.shakacode.com/
https://forum.shotcut.org/
https://forum.sigur-ros.co.uk/
https://forum.silverstripe.org/
https://forum.sketchfab.com/
https://forum.slots.lv/
https://forum.smallgiantgames.com/
https://forum.snap.berkeley.edu/
https://forum.snapcraft.io/
https://forum.spinitron.com/
https://forum.starkeeper.it/
https://forum.storj.io/
https://forum.sublimetext.com/
https://forum.tailscale.com/
https://forum.talksurf.com/
https://forum.tudiabetes.org/
https://forum.tzm.community/
https://forum.ubiquityrobotics.com/
https://forum.ui.vision/
https://forum.uipath.com/
https://forum.voyeur-house.tv/
https://forum.vuejs.org/
https://forum.waypoint.vice.com/
https://forum.webflow.com/
https://forum.xboxera.com/
https://forum.yugabyte.com/
https://forum.yunohost.org/
https://foorumi.katiska.eu/
https://forums-daip.ac-lille.fr/
https://forums.abeja.io/
https://forums.ageofempires.com/
https://forums.albumoftheyear.org/
https://forums.anki.com/login
https://forums.ankiweb.net/
https://forums.askmrrobot.com/
https://forums.babypips.com/
https://forums.balena.io/
https://forums.bignerdranch.com/
https://forums.blinkstick.com/
https://forums.cfl.ca/
https://forums.cgsociety.org/
https://forums.developer.nvidia.com/
https://forums.docker.com/
https://forums.envato.com/
https://forums.episodeinteractive.com/
https://forums.eveonline.com/
https://forums.expo.dev/
https://forums.expo.io/
https://forums.fast.ai/
https://forums.flightsimulator.com/
https://forums.flixel.com/
https://forums.fsharp.org/
https://forums.funcom.com/
https://forums.gearboxsoftware.com/
https://forums.ibboost.com/
https://forums.ideacity.ca/login
https://forums.idiox.io/
https://forums.improbable.io/
https://forums.lawrencesystems.com/
https://forums.medicalschoolhq.net/
https://forums.metallica.com/
https://forums.nyheritage.org/login
https://forums.paddling.com/
https://forums.pimoroni.com/
https://forums.playlostark.com/
https://forums.plex.tv/
https://forums.republicwireless.com/
https://forums.sandisk.com/
https://forums.serverbuilds.net/
https://forums.sketchup.com/
https://forums.splashdamage.com/
https://forums.spongepowered.org/
https://forums.steinberg.net/
https://forums.swanlibraries.net/login
https://forums.swift.org/
https://forums.t-nation.com/
https://forums.tapas.io/
https://forums.theanimenetwork.com/
https://forums.urbackup.org/
https://forums.visual-paradigm.com/
https://forums.wyzecam.com/
https://fossresponders.discourse.group/
https://foundation.discourse.group/
https://free.discourse.group/
https://futuredemocracynetwork.involve.org.uk/login
https://gestgov.discourse.group/
https://github.community/
https://gpusph.discourse.group/
https://gramps.discourse.group/
https://greyarro.ws/
https://hairtell.com/
https://healthforum.nz/
https://help.imgur.com/hc/en-us
https://help.nextcloud.com/
https://hitobito.discoursehosting.net/
https://housing.atpflightschool.com/
https://idd.org.uk/
https://ideas.weloveideas.com/login
https://igraph.discourse.group/
https://im-lichtenhain.de/login
https://insiders.infosecinstitute.com/forum/c/infosec-skills-knowledge-base
https://intfiction.org/
https://itsfoss.community/
https://kanboard.discourse.group/
https://keycloak.discourse.group/
https://labs.daemon.com.au/
https://librepcb.discourse.group/
https://lighttable.discourse.group/
https://linux-tips.com/
https://llvm.discourse.group/
https://lookmumnocomputer.discourse.group/
https://lpunderground.com/discourse/
https://mapwindow.discourse.group/
https://mediasoup.discourse.group/
https://meshtastic.discourse.group/
https://meta.discourse.org/
https://mixomics-users.discourse.group/
https://moddio.discourse.group/
https://molochdao.discourse.group/
https://monitoring-portal.org/
https://monkeydev.discourse.group/
https://monocycle.info/
https://nomadlist.com/
https://nornir.discourse.group/
https://ns-community.folio3.com/login
https://omforum.sr.de/login
https://onehack.us/
https://openclimatefix.discourse.group/
https://openhealthhub.org/
https://opennms.discourse.group/
https://openstagecontrol.discourse.group/
https://openvidu.discourse.group/
https://osclass.discourse.group/
https://osqp.discourse.group/
https://peshkupauje.com/
https://phaser.discourse.group/
https://poppy.discourse.group/
https://precice.discourse.group/
https://pressbooks.community/
https://psychtoolbox.discourse.group/
https://pyopensci.discourse.group/
https://qubes-os.discourse.group/
https://quelea.discourse.group/
https://react-native-webrtc.discourse.group/
https://realtimevfx.com/
https://reflector.sota.org.uk/
https://research.acronis.com/login
https://revolutionrobotics.discourse.group/
https://rexkrueger.discourse.group/login
https://rpforum.30cm.org/login
https://rust-audio.discourse.group/
https://sapienmedicine.discourse.group/
https://scammer.info/
https://scanpy.discourse.group/
https://se23.life/
https://sellercentral.amazon.com/forums/
https://sirix.discourse.group/
https://sleuthkit.discourse.group/
https://soaps.sheknows.com/message-boards/
https://socialhub.activitypub.rocks/
https://source.checkmarx.com/
https://spamlogger.com/
https://spout.discourse.group/
https://staging-community.markforged.com/login
https://statically.discourse.group/
https://stimulus-reflex.discourse.group/
https://studmed.dk/
https://support.glitch.com/
https://support.ibiblio.org/
https://support.ilovegrowingmarijuana.com/
https://swapd.co/
https://sweatco.in/
https://swi-prolog.discourse.group/
https://talanoa.sprep.org/
https://talk.commonmark.org/
https://talk.folksy.com/
https://talk.icam.com/
https://talk.jekyllrb.com/
https://talk.jsonline.com/
https://talk.macpowerusers.com/
https://talk.manvfat.com/
https://talk.mylifeelsewhere.com/
https://talk.remobjects.com/
https://talk.sleepapnea.org/
https://talk.thereserveforce.com/
https://tappara.co/
https://tech4goodlabs.discourse.group/
https://thepavilion.io/
https://tmw-forum.discourse.group/
https://travis-ci.community/
https://trio.discourse.group/
https://twittercommunity.com/
https://ubuntu-mate.community/
https://unicyclist.com/
https://us.forums.blizzard.com/en/blizzard/
https://users.imba.io/
https://users.rust-lang.org/
https://users.scala-lang.org/
https://vaperina.cc/
https://wazo-platform.discourse.group/
https://wiki.keyboardmaestro.com/
https://wled.discourse.group/
https://www.airlinepilot.life/
https://www.atlasobscura.com/forums
https://www.chiefdelphi.com/
https://www.discourse.org/customers/patreon
https://www.feverbee.com/communities/examples/platform/discourse/
https://www.finalbuilder.com/forums/
https://www.freecodecamp.org/forum/
https://www.gamekult.com/forum/
https://www.helloforos.com/
https://www.ilance.com/
https://www.ketogenicforums.com/
https://www.mongodb.com/community/forums/
https://www.ruby-forum.com/
https://www.secopshub.com/
https://www.silver-collector.com/
https://www.sitepoint.com/community/
https://www.survivefrance.com/
https://www.synovialsarcomasurvivors.org/
https://www.thethingsnetwork.org/forum/
https://www.thewonderweeks.com/
https://www.twit.community/
https://www.webwinkelcommunity.nl/
https://www.wer-weiss-was.de/
https://www.zbrushcentral.com/
https://zegist.com/
https://zigbee2mqtt.discourse.group/
https://zola.discourse.group/