Kickoff is a collaboration tool specifically aimed at small groups, like an app development team. The app offers centralized to-do lists, notes, file management, and instant messaging.
I’ve not used it effectively yet, but the app definitely seems to offer a nice hands-on approach to collaborating. That, and the app’s pixels were pushed and glued together by two perfectionists: Benjamin de Cock and Michaël Villar.
Definitely worth checking out if you are going to work on a project with a small team, especially for a side project.