SharePoint Offline Synchronization with Colligo Reader

With this free tool, You can connect to a SharePoint site and download the documents and Lists to your local machine and access them offline. There is an another product from the same vendor, Colligo Contributor, which allows two way sync with SharePoint and which is not free.

By the way, we have SharePoint Workspace 2010 (which is successor of Microsoft Office Groove 2007) which supports two way sync but not a free product. 

Download URL: https://www.colligo.com/products/colligo-briefcase/

Disclaimer: By writing this, I'm not endorsing this product by anyway :-)