Seafile — Open Source Cloud Storage App

Client for the Seafile cloud file server and project management software. If you are in a small team with a few people, you can create a group in Seafile and invite other team members. Team members can then maintain file libraries together and collaborate around them. You can try the demo, sign up for an account at the website, or since the server-side is also free-as-in-freedom, it can be installed on any server and configured to work with the app.