From the README at the current published commit:
The current focus is on implementing next-word suggestions, which has become complicated/hit a snag and is taking more time than originally planned. Updates will come when this issue is resolved. Thank you for being patient.
Prior to this, releases occurred quite regularly.
I recommend using Molly instead if you need to communicate with Signal users. Note, the Molly-FOSS flavor excludes proprietary Google libraries entirely.
If you are interested in trying an alternative that is unrelated to Signal, I suggest looking at SimpleX Chat.
Just FYI, Signal (Open Whisper Systems) is not FOSS-friendly. The server-side software is not open source, they refuse to federate with other Signal implementations, and they are unfriendly to forks. See:
It’s not exactly what you’re wanting, but there is Remote Video Camera on F-Droid.
If I were doing it, I would look for an app that just implements the same basic functionality as a network-connected camera. Then video storage, alerting, motion detection, etc. would all be handled by something like zoneminder.