This is a client for connecting to current mainframes like https://irata.online/.
There is no .deb or snap for this one, only sources in a bz2. The dependencies appear to be libsndfile and libSDL according to the README.
There are clients for Apple II, ZX Spectrum, Commodore 64, Amiga, Atari ST, Android, PC & Mac. It would be great to be able to participate on Ubuntu etc.