Cage is a an online collaboration tool that makes it shockingly simple for designers and teams to share, organize, manage, and approve creative work. Using Cage, you can add simple, straightforward notes & conversations directly on the work, and then show your clients past revisions so they can see the progress you have made.

Cage provides your clients and team the ability to approve work faster. It is useful for any type of designer, artist or creative team without a lot of clutter. Leaving out vital features for the sake of simplicity leads to workarounds, and that doesn’t work for anyone. It makes it easy for creatives to present, manage and secure approvals on their work

I really like the user-interface of Cage. It looks really clean, nice and professional. Cage is 100% free while in beta. You can give it a go and see if it fits your needs.

Requirements: -
Demo: http://cageapp.com/
License: License Free