Mainly the project manager.

> What about user testing and customer development?

Testing could be done by everyone, mainly the project manager, although you could perhaps add a tester to the team. Don't know what customer development is.

> By “graphic design”, do you mean User Interface design? If so, who is responsible for the user experience beyond just UI?

Yes, UI design. The graphic designer would be primarily responsible for UX, but also the project manager and developers.

This is based on my experience with mobile app development. Right now, it's a fairly complex product, users often say that it's much better for many use cases than the alternative by Google, which I guess may be developed by a 10x larger team.

Rode map is just: keep it working, or whatever EM twitted about hour ago :)

But I agree it's way to optimistic number. You need at least a few for each platform, just because of bus factor, you also need people to keep in touch with Apple/Google reps etc., making sure bills are paid etc.

I imagine it will mostly be just minor tweaks and no major features, you can easily do both mobile targets by cca 10 people, not working crazy hours. There are plenty of successful apps with smaller teams, that make it work.

Eh, tossing the direct comparison to Twitter out here because they seem to have gone too far the other way, this is much like saying "I can make 1,000,000 screws a day, so assembling at least 100 cars a day should be easy".

I am not saying that writing twitter like app is easy, but writing it and keeping it running are two different things.

If you are not adding new features, you are just mostly keeping up with Android/Apple platforms, which can be annoying, but not that difficult.

> also need people to keep in touch with Apple/Google reps etc.

You certainly don't need people specifically for this task.