I have nothing but praise for Matrix, via element.io or any other client of your choice. It's user-friendly, mature, history is not restricted, and the public m

I have nothing but praise for Matrix, via element.io or any other client of your choice. It's user-friendly, mature, history is not restricted, and the public matrix.org homeserver works great. You can use Element in your browser or as an Electron app. We've been using Matrix for a couple of years for the project I work on (Exosphere). It's a much better fit for open, public communities than Slack is (or Discord for that matter). Matrix lets you have both public, non-encrypted rooms, and end-to-end-encrypted DMs (and private rooms) where the server doesn't see the content of messages. You can organize a collection of rooms in a "space" for your community. To ease the migration for your existing Slack users, you can even bridge Matrix channels to Slack channels, so people in either place still see all the messages.