Jami is a free/libre, end-to-end encrypted and private communication platform that requires no central authority. Jami’s features include: text chats, voice and video calls, screen sharing, file sharing, conference calls, and group chats.
Why I think this tool should be added
There is only one recommendation for a Discord alternative and it isn’t popular. This one doesn’t require any personal details and guarantees E2EE, unlike some Matrix clients which don’t universally support E2EE.