Cloud Sharing

Hello, I need a file synchronization system based in 3 different plattforms: web (PHP), windows (.NET) and MacOS. The system shoud be capable of syncing files and folders in a selected folder (just as dropbox does). Files should be storaged in Amazon's S3 plattform. It must use files delta compressing to save data transferences and to have a file history. Desktop applications (Windows and Mac) must be able to select the syncing folder, to display a small icon in each file to tell file's status. And display in a window a chat and other options for each file and folder. The system must be able to share folders between users, and to ask users to share a folder. More details will be given in case you are interested. Payment won't exceed 1,000 USD.