Dropbox - Online Sync and File Sharing
Beyond Compare - Beyond Compare allows you to compare files and folders.
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.