Download Briar Desktop for Linux, Windows and macOS - Briar

It'll sync history for forums and private groups. Since there's no "login" it is a different account on every device you use, so there's no history on individual chats to sync. I think this makes private groups a little more useful because you can have multiple logins on a single group to communicate with others on that same group. A little clunky but way more secure than anything else out there.