Acid Rain is an application that lets you synchronize files between computers and keep a history of changes in them.

Acid Rain uses Mercurial technology to keep files, this makes possible to use it independently on a single computer to keep the history of different versions of your documents or with an external server to synchronize your files on different PCs. Theoretically you can use any Mercurial hosting service. Another option is to build your own server using Acid Rain Server and synchronize your files across multiple computers via your local network or even the Internet.