Just because you didn't mention it, Matrix https://matrix.org/ https://matrix.org/ is another option. It supports federation, services (like IRC bridges), encry

Just because you didn't mention it, Matrix https://matrix.org/ https://matrix.org/ is another option. It supports federation, services (like IRC bridges), encryption, push notifications, offline storage and has some really nice clients for Android and iOS. I found it really cool that I could spend ~half an hour setting it up on my own server then just pop in on chats on another server.