Who doesn't like free online games? Using a browser and programs like Flash, Java, and Shockwave, you can turn your PC into a free arcade! In addition, there are some free full versions of old games (released for free legally by their owners) that will allow you to delve into the past to play some of the best games ever without spending a penny. 

Free Online RPGs 
Free multiplayer online games with RPG elements. 

Betrayal At Krondor 
No, this is not a demo. This is the FULL game of one of the greatest RPGs ever. Sierra released this one many moons ago to hype its Betrayal in Antara game.

Free Arcade 
Play several different free games such as Muy Thai, PaintBall, Tanks, and Pipe Mania.

GameOgre Arcade 
Compete for the high score in such games as Tetris, Moon Lander, Stick RPG, and Flames of Fury.

Starsiege: Tribes
Graphics: 3D
Download: Yes
Type: Full Version
Not only one of the greatest multiplayer shooters ever, but also one of the first games that had to be played on the Internet or a network. 

XU4
Graphics: Yes
Download: Yes
Type: Open Source
Ultima 4 recreated to run on newer systems. This site also has the original DOS version of the game and even the graphics upgrade for it.

Savage
Graphics: 3D
Download: Yes
Type: Full Version
Part real-time strategy game and part first person shooter. The full version is now available for free after releasing a sequel. 

America's Army
Graphics: 3D
Download: Yes
Type: Full Version
Download the full version of one of the best multiplayer shooters available. This game is given away free to help army recruitment.

Railroad Tycoon
Graphics: 2D
Download: Yes
Type: Full Version
Download one of the all-time best strategy games. This game is given away to help promote Sid Meier's Railroads.

Freeciv
Graphics: 2D
Download: Yes
Type: Open Source
Empire-building strategy game where the goal is to lead your tribe from the stone age all the way to the space age.

FreeCol
Graphics: 2D
Download: Yes
Type: Open Source
Turn-based strategy game based on the strategy classic known as Colonization. The goal is to bring a nation to independence. 

Alien X
Graphics: 3D
Download: No, Browser
Type: Flash
First person shooter (FPS) with impressive graphics and a nice selection of weapons.

Grand Theft Auto
Graphics: 2D
Download: Yes
Type: Full Version
The game that started the controversial blockbuster franchise in its entirety for free. The size of this file is 328MB.

Glest
Graphics: 3D
Download: Yes
Type: Open Source
Glest is a free real time strategy game, available for several operating systems and that can be modified using XML and a set of tools.

Kuma/War
Graphics: 3D
Download: Yes
Type: Full Version
Former subscription-based shooter that recreates real-life war events. This game is episodic.

Neocron Arcade
Graphics: 2D
Download: Yes
Type: Full Version
Arcade-type shooter that is based on the MMORPG known as Neocron. You kill mutants as Agent Jones. 

Wolfenstein Enemy Territory
Graphics: 3D
Download: Yes
Type: Full Version
What started out as being a multiplayer addition to Return To Castle Wolfenstein was released as a stand-alone free multiplayer game.