[Freemium][1] - Make the bulk of your game available for free, but provide paid premium content (e.g. *Fantastic Contraption* and *Quake Live*)

[Adware][2] - Make your game completely free, but with adverts.

[Subscription based][3] - Players pay a regular subscription fee to play (e.g. most MMORPGs)


  [1]: http://en.wikipedia.org/wiki/Freemium
  [2]: http://en.wikipedia.org/wiki/Advertising-supported_software
  [3]: http://en.wikipedia.org/wiki/Subscription_business_model