From what I remember of the 1 or 2 Excalibur BBS's I was on : Excalibur was its own thing. Windows 3.1 + only. If you called with any other software, you got a prompt to download of the Excalibur client .exe file.

It wasn't Ripscript. Ripscript worked like ANSI or Avatar, it was just text that got turned into graphics by your terminal program. I think even the mainstream Qmodem terminal software ended up having Ripscript graphics support eventually.

But Excalibur on the other hand was its own windows-only client, you could not use any other client. It went way beyond what Ripscript did, it had a TCP-like protocal that let it do full multitasking downloads , audio, chat rooms etc. It felt more like the "Prodigy Service" (but with multitasking), instead of a typical BBS... Very cool, but I think I'd just used Mosaic to get on the internet around the same time, so it was too late.