open source, self-hostable, federation coming in the future looks and feels super similar to Discord freemium but premium features are free if self-hosted a little slow right now because of a influx of users because of the recent Discord controversy

open source, centralised great alternative if you use Discord only for chatting and calling with friends or small communities which don't require multiple channels supports now group calls with a link (so you don't have to join a group) free

open source, self-hostable, federated (uses e-mail infrastructure) same use case as Signal but decentralised