Movim - An open-source, federated and encrypted Text Chat & Video Call (w/ screenshare!) platform made in France since 2010

It's quite an impressive little app. Under the hood, it's an advanced XMPP client that has:

• Excellent text chats with file upload support, including solid optional encryption (OMEMO, based on Signal's encryption but modified to be compatible with federation)
• Group voice/video calls with screensharing (must use a chromium based browser to screenshare an app's audio at the moment)
• A neat integrated blogging feature for communities & individuals
• a fun built-in paint program to draw stuff into the chat
• Full working and proven federation thanks to the XMPP back-end, which allows it to scale up reliably and easily self-host (XMPP is very lightweight).
• Uses the AGPL license, ensuring that cropos won't be able to take it over. It'll be community-owned forever.

In message-mode, it looks fairly similar to Discord:

If you're curious if it'd work as a Discord replacement, it's still missing Discord-like servers with collections of rooms in them, as well as drop-in voice rooms. However, the developer is actively working on implementing those features, with the server w/rooms part likely to be implemented within the next few weeks. They already posted what it looks like in the development branch:

To stay updated on its progress, the !xmpp@slrpnk.net community pretty reliably posts news about it.