Guardian of Forever BBS, which features Star Trek and Atari-themed artwork, animation and sound effects encoded in the Instant Graphics and Sound format for the Atari ST.
Introduced in 1988, the IS graphics language provides a way to encode vector graphics, sound effects, and animation effects as ASCII text which can be served by text-based Atari ST BBSes. It probably inspired the later RIPscrip format.
To see IGS content when connected to a BBS, users must run the IS desk accessory on their Atari ST computer or emulator. Note: Parts of this login sequence require IGS v2.19, which is still in beta. You can download v2.18 (released on New Year's) on Break Into Chat