The core uSync package lets you sync all your settings and config to and from disk, it is great for simple deployments and source control. Its open source and free.
Content Edition adds the ability to sync Content, Media, Dictionary Items, and domain settings to your standard uSync folders, it is open source and free.
uSync Complete adds a suite of extra features to uSync, including uSync.Exporter, uSync.Snapshots, uSync.PeopleEdition and uSync.Publisher. offering you a comprehensive set of tools to manage and deploy your Umbraco Sites.
Installing uSync.Complete will give you all the uSync tools (including the core and content edition packages) its the only install you need to get everything.