The open source real life meetup platform @GetTogetherComm has quite a few groups already:
If you want to just see groups near you, go to the instance's front page at:
You can also set up your own group. (Unlike meetup.com there are no charges on #GetTogether.)
At the moment groups are mainly about computing, but there's no restriction on the topics a group can cover.
mastodon.at is a microblogging site that federates with most instances on the Fediverse.