Scratchix is a Facebook application, but also has a stand-alone website.
Players can win money and prizes by scratching cards they received for free. Extra scratch cards can be obtained by completing surveys and offers (also free).
Scratchix was launched in January 2009 and reached 200.000 users in its first year, of which 40.000 use the application at least once a month.
Link: Scratchix on Facebook or Scratchix website