I love Trello for collaborating. It is free and runs on just about every device. I don't know how complicated your projects will be, but is is very flexible and the api is a dream to work with. If you go the Trello route, you can review time spent on tasks in many ways at reportsfortrello.com. (I created the site.)

I would also recommend google hangouts if you aren't using it already.

Best of luck!