It's easy to extend Spree by writing your own extension. There are already over one hundred third party extensions listed in our official registry.
F.Connect - Online store and widgets on Facebook Create your store to Facebook and create product widgets for your Fan Page
Spree Social (Offfical) Adds social network login services (OAuth) to Spree
spree-facebox Allows to view product images in a facebook-like lightbox
facebook_connect Facebook Connect extention to Spree