I probably would happily use hosted solutions, but being in China, everything is either completely blocked, half-works, or way too slow. So we (have to) use Gogs[1] as own Github, Mattermost[2] as own Slack, and StandardNotes[3] as own Evernote (Evernote has China presence, but it's a slightly different product + privacy concerns). I'm also quite happy with Haraka[4] mail server for outbound emails as a self-hosted Mandrill / Mailgun alternative.