Bootstrapped a fitness app (Bruiserfit - https://bruiserfit.com/) with a friend based on my own measurable high-intensity physical training workouts. We built the first version not really knowing what we were doing, slapped AdWords on it, but users never came. We couldn't get past the activation phase - the initial product wasn't intuitive and compelling people to workout is challenging. Over the past couple years we've iterated on the user experience to an adequate state, but we still lack retention. It seems like the format is still confusing for beginners and that most people simply don't want to train themselves to do tough, fast bodyweight workouts.

On the technical side, we used Rails 5 and followed the Thoughtbot playbook. But neither of us were very experienced in native development, which prevented us from offering many of the bells and whistles that other market offerings provide. If I had to do it all over again I would probably give it a shot with React + Firebase.

Like others have said here, democratically running an equally shared company with friends sounds better on paper than it is. Different personal beliefs and approaches often lead to deadlock. Communication is essential to avoiding resentment. It gets easier with practice, but there was still too much to juggle for us and not enough time, know-how, and motivation.

We still casually hack at the project on the side. My cofounder and his wife swear having the project on his resume landed him his current and very comfy gig. I'm still waiting to see if anything beyond the experience itself comes out of it for me.