Put away your wallet and step back from the $50 games that line store shelves. The GNU… Put away your wallet and step back from the $50 games that line store shelves. The GNU Public License was designed to provide free and legally downloadable software to the computer-enabled masses.

Its tenants include shareable open-source code, platform independence for the equal freedom of Mac, Windows and Linux users, and general availability – the files reside on an easy-to-use website.

The GPL is used commonly for amateur-programmed software created to further the use and promotion of open-source operating system platforms, but it can also be used for legacy games or games deemed too old to bring in money.

It is in this use that the story of the “liberated games” comes in. Companies like Raven Software and ID Software, the creators of the original first-person shooters, have decided their games from the early ’90s can no longer hold their own in the modern commercial world of intense graphics and highly accurate animated gore.

Therefore, they decided to “liberate” their games and make them fully available on the Internet for people to download, install and enjoy.

This is, of course, not really news. Some games have been liberated since the turn of the century. Unfortunately, many of these great games have been completely forgotten, and people are spending more of their time burning out their graphics cards with “BioShock” than they are just killing demons with “Doom.”

The time has come for gamers to return to the early ’90s. Many of these throwback games will work on Microsoft Windows XP, Mac and Linux. Still others can be run through emulator programs like DOSBox.

The biggest contenders that many have forgotten are open-source and freely available are the first two games in the “Doom” series by ID Software. Arguably one of the first first-person shooters, the “Doom” game attempted to provide a rich, three-dimensional world for the player to run around in. The player progresses through the technological realms of the ethically-ambiguous Union Aerospace Corporation to the brink of hell to face the devil himself. Both “Doom” and its successor “Doom II” are available under the GPL for download. Ports are available to run on Windows XP, Windows Vista, Macintosh OS X and Linux.

Similar games, like “Duke Nukem 3D,” a popular first-person shooter from 1996, are available under the GPL license. For players who want a just a little bit more than “Doom,” “Duke Nukem 3D” should stand as an excellent alternative.

Its game engine is one step better than “Doom,” and allows for better environment interaction and more complicated, realistic map design. More things tend to blow up in “Duke Nukem 3D” than in the “Doom” series.

Additional licenses, other than the GPL, are available for freely open-source software. Many companies have provided their own licenses, which, like GPL, provide for the distribution of software source. Popular 3D science fiction games like “Descent” and “Descent II” are distributed under the “Descent License,” and are therefore free to download and distribute.

“Hexen,” another 3D first-person shooter, is available under the “Hexen/Heretic License” along with its cousin, “Heretic.” Both games are similar to “Doom” in engine, but tend to have a more complicated storyline.

Some might think these old games are too pixilated to be fun to play. They would much prefer the better, crisper graphics of more modern games.

Fortunately, the makers of these games have considered this problem. Many games, like “Doom” and “Quake” have available high-resolution packs, giving them crisper graphics for more modern computer platforms.

Games that don’t have resolution packs can be forced into higher resolutions by better graphics cards – at higher resolutions, the graphics appear smooth, yet crisp and infinitely more attractive.

Because all of these games are open source, they are also customizable. Gamers with a programming bent can sift through the original ID or Raven Software code and change minor elements.

Players have also hacked the Doom WAD standard, allowing them to edit maps and customize environments. “Doom,” “Doom II,” “Hexen,” and other games that utilize the “Doom” engine, can all be customized easily with downloadable editors.

To obtain many of these games, their high-resolution packs, and any editors you wish to utilize, a simple Google search is required.

There you’ll find many ports for each game, depending on which operating system you wish to use. For Linux users, “PrBoom” provides an excellent, stable platform through which to play the original “Doom” series. “Doom Legacy” will support Windows and Macintosh OS X players. For all other games, simply search Google for “liberated games.”