Thanks. There was a config error blocking the certificate renewal. Note that this site is pretty outdated and quite likely will go offline soon as the old servers are EOL. swish is more or less the followup of pengines.
The Pengines library is part of the core and considered a stable and vital library
SWISH indeed runs on top of library(pengines)
pengines.swi-prolog.org demonstrates another way to build applications on top of the Pengines platform. Most of that is now accessible under SWISH as well. SWISH allows for a notebook to contain a single HTML cell and be opened in whole-screen mode. This allows for running an application where the Prolog interaction has become invisible.