We have mentioned in the past a few times that it is a common misconception that FOSS games need to be also "freeware", and in fact the opposite can be quite beneficial to the overall development of a game or the engine it is build on.
The 2D jump & run Frogatto & Friends has been for sale on mobile platforms for a while now, and its really high quality game-play and graphics are definitely a notch above most other open-source games:
All of it is possible through the use of their awesome open-source engine Anura.
Now they are looking to sell their game also on desktop computers through the very popular Steam digital distribution platform. You can vote for inclusion here.
As far as I am aware this is the first open-source game that actually aims to be sold through this channel, but recently another one, Warsow, was actually approved for inclusion as a freeware title.
As a launch of their "greenlight" campaign, the creators of Frogatto & Friends have started a Q&A session on reddit, where you can learn more about them and their awesome game(s).
Unrelated to that: please also check out our own "sub-reddit" about open-source gaming :)
Free, libre games and development news