My choice, because it's the stack I know very well, would be Prosody ( https://prosody.im/ https://prosody.im/ - I'm one of the devs) and a web client such as C

My choice, because it's the stack I know very well, would be Prosody ( https://prosody.im/ https://prosody.im/ - I'm one of the devs) and a web client such as Converse.js ( https://conversejs.org/ https://conversejs.org/ ). XMPP is highly extensible, Prosody is highly modular, which make them a good foundation for building on top of. That said, the right stack is generally the one that matches your requirements, and (if this isn't primarily a learning exercise) whatever you're most familiar with. The hardest part of building a Discord or Slack-like in 2022 is actually not the technical stuff. There are many comprehensive open-source products already out there that compete with these companies, such as Mattermost, RocketChat and Element.