There were plenty of Atari ST BBS games back in the day, but I only know of one which came with a graphical front-end client: Thieves Guild.
It took me a long time (and required real hardware) to be able to actually play it.
Once I obtained a Mega STe, I wanted to make a video showing what the Thieves Guild front-end looked like in action.
The CosmosEx's new remote screencast made that a possibility. Here's my first attempt: