IO Games

I've noticed Product Hunt has added a few gamification features like the "streak" on the landing page as well as badges for the profile pages. I think they are well done because they encourage the behaviour the platform wants to see and at the same time they aren't in your way. The "core" experience of Product Hunt always had a strong game-loop thanks to the upvoting and daily ranking dynamics but it is interesting to see these core ideas still being fleshed out more and more over time. Well done! Question: have you come across other apps or platforms that do gamification really well? Where it feels like part of the thing and not just like a gimmick? Any pointers appreciated!