The Quake III Arena "engine" has been released as GPL free software code, continuing id Software's tradition of releasing their older software to the public for free (as in libre) use. Why is this interesting? Because what they're doing isn't giving away an old game that nobody would buy, they're giving away a toolkit for virtual environments that is much more sophisticated than casual observers might expect.
For those of you who aren't familiar with the genre, Quake III Arena is the third iteration of the "Quake" series of first-person shooter computer games. The "Arena" aspect means multiplayer capacity is built-in; with very little difficulty, a dozen or so friends can connect over a network and play against each other. By releasing the source code under the GNU General Public License, Id Software isn't making the game itself free to download -- the various textures and maps and sounds remain proprietary. All that has been released is the "engine:" the core software that controls things like the physics model, the interaction between objects, player motion, networking, communication between players, and so forth.
What this means is that developers can use the Quake III Arena engine along with their own graphics and maps to create their own virtual worlds.
The vast majority of software coming from this release will be derivative games, or tweaks to the Quake III engine to make it run faster or on new platforms; Quake III already runs on Windows, Mac and Linux, but id Software founder John Carmack argues that mobile phones are getting close to the point that they'll have the hardware to run something like Quake III. Once mobile phones can run it, multiple other devices will be able to, as well. (To see an example of this progression, check out It Plays Doom -- a website devoted to listing the myriad devices, from iPods to PDAs to phones (and more) able to run ported versions of the game Doom, an older first person shooter game from Id.)
But that doesn't mean that games are all that can be made. Consider: abstractly, the Quake III Arena engine is a compact, multiplatform system for multiple users to share an interactive environment with controllable physics. Just because the original version included shooting at each other doesn't mean that every iteration has to. A Q3A-derived environment could just as easily be a virtual meeting space, an environment in which to demonstrate physics principles under un-Earthly conditions (how would it feel to run and jump on Mars? Why is zero-gravity hard to move around in?), or a set for virtual moviemaking. This last, referred to as "machinima," will be the subject of an upcoming piece on WorldChanging, or so Emily promises.
Mostly, I find this interesting because it's an example of how proprietary and free code can co-exist in a larger software ecosystem. Id recognizes that some people will play free games derived from the Quake III code release instead of purchasing Quake 4, but also knows that many more will end up having a greater interest in Q4 based on their experiences with Q3-derived code. Moreover, Id also sees this as a way of encouraging coding creativity; it's a platform to try something new and unexpected, which is good for the industry as a whole.
