Very nice suggestions for newbies! I have yet to join a contest myself, maybe that's next. But yeah, finding a community really is the key to enjoyment.
Hrmm suggestions... A natural segueway would be to explore the side projects.
One slight tweak to utopian: it uses GitHub so I wouldn't say it's a decentralized GitHub. I would just say it rewards Open source contributions.
Also don't forget zappl and steepshot, and maybe even this one I just stumbled into.
Those are some good suggestions. Zappl looks like blockchain Twitter and Steepshot like Instagram. The Q&A app looks really interesting. I'm going to try it out. Thank you!