Dropbox allows you to sync your files online and across your computers automatically. With Dropbox sharing files is really simple. You just have to create folders and to share them with people of your choice. You can then collaborate on the same files. You have full control to who has access to your shared folders. In case of problem, you can kick people out and remove the shared files from their computers in the process.
Dropbox works just like any other folder on your computer, but with a few differences. Any files or folders inside Dropbox will get synchronized to Dropbox's servers and any other computer linked to your account. Green checkmarks will appear on top of your files to let you know that they're synced and up to date. All data is transferred over SSL and encrypted with AES-256 before storage. Dropbox keeps track of every change made to any of its contents.