Previously Sync Framework required  a Windows  machine with Sync runtime installed on the client side. The Sync Framework 4.0 now leverages a remote sync service and hence any client that speak HTTP and OData can build occasionally connected  applications by leveraging Sync Framework.

Here is a link to the official blog post: http://blogs.msdn.com/b/sync/archive/2010/10/28/announcing-sync-framework-4-0-october-2010-ctp.aspx.

- Hanu