Ask HN: Recommendation for open-source self-hosted collaboration software

Hey HN guys,

there are dozens of open source self-hosted collaboration solutions. Can you recommend any of them you have good experience with?

Required standard features like upcoming events, calendar, mail integration and notification, document and contact details sharing, discussion boards, internal wiki, possible attendance system integration.

Community is from non-technical people so it needs to have user friendly GUI (CLI interface not needed). Solution needs to be open-source and self-hosted.

Thanks