Attention: Umbraco 7 documentation
uSync v4.x is a package that works with Umbraco 7.6 - 7.15, for the Umbraco 8 version of uSync, see the Umbraco 8 docs
uSync is a database / file syncing tool for Umbraco. It makes source control and deployment easier, because you only have to worry about changes on the disk - and let uSync do all the database stuff.
The best way to get uSync is via NuGet
If you want you can get it from Our Umbraco