We are trying Bootcamp this year. It is an online project management service that is free for schools.
https://basecamp.com/
The jury is still out, but it is looking promising. You can use your normal computer or the mobile device app.
It is possible to set up multiple sub-teams and/or projects with milestones and dues dates with scheduled prompts for everyone to add their input/update. It also has several areas for online messaging and brainstorming. It also allows for file uploads and linking to google docs.
So far I am pleased. Check out the video on the link I posted.