3 rounds interview
1. Skype call with HR:
Questions were mostly about me - my skills, experiences, if I can work under pressure. I think that they just want to know what kind of person you are and if you can get well with rest of the team.
2. Coding challenge - DTT's existing project
I had exams in school at the time, but I think that I finished it in one or two weeks. Lead programmer sent me feedback and after I incorporated feedback into the test, they invited me to next interview.
3. Skype call with HR, lead programmer and CEO
Lead programmer gave me again some feedback and then just discussion with HR and CEO about work (working hours, money..)
I think that there is possibility that you will have also some technical interview with some of the lead programmers if they are not sure about your test.