Another good one is Rocket Chat. It’s the most feature complete alternative I’ve tried. And there’s Mattermost and Session, although that last one’s a bit different, it’s a fork of Signal so there are invite-only groups, no list of channels, and you don’t see people come online or go offline. Out of these, only Rocket Chat has an established userbase, the others are more focused on self-hosting or creating your own group.
Another good one is Rocket Chat. It’s the most feature complete alternative I’ve tried. And there’s Mattermost and Session, although that last one’s a bit different, it’s a fork of Signal so there are invite-only groups, no list of channels, and you don’t see people come online or go offline. Out of these, only Rocket Chat has an established userbase, the others are more focused on self-hosting or creating your own group.