Asklemmy

You could probably do a Meetup clone; I think some stuff for that use case might exist already.

Friend finding would require some kind of matching engine, but what you are matching people on might be somewhat sensitive. You want to find all of the bronies without revealing that you are a brony yourself. So you can't just ship all the stuff to any instance that rolls up and says "hey I have ten thousand bronies in here, tell me all the bronies you have". You need some kind of fancy multi-party computation stuff to do distributed matching.

And then with dating you have the same problems but also your data is even more secret and your happiest users tend to immediately quit.

So what I've seen, there are already a lot of home grown dating apps, the problem is that they don't have a huge user base.

For example I joined a nerd focused dating app and got one message a month later (I also reached out to a lot of people).

So I think it can be done but the real question is how to generate a large enough user base to make it useful...