While extremely robust (comes with features like resource loading, advanced task management, burn-down charts, etc.), we've also found Binfire to be wonderfully easy to use and grasp from the get-go. It's a comprehensive platform where global teams can both collaborate and manage their projects (both on a high-level and very granular basis).
Unfortunately, they have yet to release a mobile version. Needs to happen!
Definitely give it a try and ask for help getting set up. They are extremely kind and helpful.
We're using Binfire to manage collaboration and projects between university students and professional tutors/mentors. Binfire, has streamlined that process by consolidating all of our student-tutor communications onto one platform, where everything is easily visible and managed.