This is a list of freely-licensed, open-source downloadable computer games.

Please feel free to contribute to the list, it is outrageously incomplete. The list is sorted alphabetically.

In the latest update:

• Added FlightGear.
  
• Added Rigs of Rods.
  
• Added rating for LinCity.
  
• Gave the "Complete Failure" title to FlightGear.
  
• Gave the "Not Recommended" title to Rigs of Rods.

F

FlightGear

FlightGear is a free, open-source flight simulator. It has a large collection of world scenery and planes available for download.
My Rating: 0.5/10
Average Player Rating: 4/10
http://www.flightgear.org/


Freeciv

Freeciv is an open-source variant of the Civilization games for the PC.
My Rating: Haven't played
Average Player Rating: 8/10
http://freeciv.wikia.com/wiki/Main_Page

Frets on Fire

FoF is simply a free, open-source version of Guitar Hero for the PC. There are addon songs and songs can generally be easy to make if done right.
My Rating: 8.5/10
Average Player Rating: 9/10
http://fretsonfire.sourceforge.net/


L

LinCity and LinCity-NG

LinCity and the improved LinCity-NG are open-source clones of SimCity.
My Rating: 4/10
Average Player Rating: 7/10
http://lincity.sourceforge.net/ (LinCity)
http://lincity-ng.berlios.de/wiki/index.php/Main_Page (LinCity-NG)

R

Rigs of Rods
(No image. Find me one, now.)
Rigs of Rods is an open-source physics simulator using vehicles such as trucks, planes, and boats.
My Rating: 3/10
Average Player Rating: 4.5/10
http://www.rigsofrods.com/


S

SuperTux

SuperTux is a clone of the original Super Mario game, except it uses an Antarctic setting and Linux's mascot - Tux - as the main character. There is a built-in level editor.
My Rating: 9/10
Average Player Rating: 8/10
http://supertux.lethargik.org/


SuperTuxKart

SuperTuxKart is a clone of Mario Kart, but uses mascots such as Tux the Penguin (Linux's mascot), Wilber (the GIMP mascot), and some elephant thing (the PHP mascot). It is 3D and maintains Mario Kart's features such as attacks, grand prix, and also has support for addons.
My Rating: 7/10
Average Player Rating: 8.5/10
http://supertuxkart.sourceforge.net/

What Qualifies as Open Source?
"Open source" refers to something that has publicly-available source code, and that the software can be modified by anyone who knows how, and development is not restricted to just one development team. Because of this, many open-source programs are moddable or have add-ons.

Anything found on SourceForge.net is considered open source because SourceForge is a host for open-source projects.

The majority of open-source software is free.