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.Some of the advantages over other similar applications are these:

• You decide how to use it, either on a single computer, only versioning  your files or in conjunction with a third party  service (Mercurial hosting) to synchronize on different computers or even more using your own server.
•  If you want to use a Mercurial hosting service, you decide the provider company.
•  If you mount your own server, you decide if access to it  through your local network or  through Internet