It packetises and encrypts chats, using email(SMTP) as the transport medium.
Sends downsampled pics, videos or push-to-talk audio by default. Can send full quality pics, videos, or attachments too, as a file.
Integrates with Jitsi Meet to connect video-calls.
It's available on F-Droid, and you can use a seperate free-email-address(100MB limit) for the SMTP backend (from https://nine.testrun.org/ ), or use your own existing email address.