[ToasterOven]

I put a decent amount of work into something similar and had a fairly polished mobile app with a good number users in a few concentrated communities using it. And it was a disaster.

Anonymity plus a shared reference point of being near each other (mine was 400ft) produced either random attempts at discussion that never matured into a conversation, or focused vitriol at real people.

We ended up discontinuing the app as it was hard to overcome the double network effect (needing people you actually want to chat with, and needing them to be nearby), and the only times where it did was because of a pretty reprehensible use case.