I initially developed Gymmr as a web app, but decided that mobile was the best platform given the increasing popularity of mobile chat apps.
https://play.google.com/store/apps/details?id=com.connecteddeveloper.gymmr
The app lets users find others who are into (or interested) in the same diet and fitness programs as they are. For example, someone who's on a ketogenic diet and doing the 5-3-1 program might want to meet people with similar plans/goals.
It is also location-based and allows people to meet others who go to their gym. The idea is to break down some of the barriers to meeting others at the gym.
I've started small, but I have future plans for Spotify integration, search, and anything that users might request.