Supporting the veryserious.website work, this is an effort to update the tooling necessary to make TTYs usable on computers again.
This is an emulator for the ANSI TIA/EIA-825 protocol, also referred to as Telecommunications Device for the Deaf (TDD) or TTY. These devices allow people who are hard of hearing to communicate over analog phone lines using a keyboard and text display. It's essentially a very simple FSK modem.