Doom is vanaf heden open-source, zo weet Voodoo Extreme te vertellen:
id Software's John Carmack has officially re-licensed the Doom source code to the GNU General Public License! For those not In The Know, the GPL license basically allows anyone to do whatever they want with the code, even modify and sell it, as long as the source remains freely and publicly available.
This means that if a person wished, they could modify the Doom source and sell a game based off of it, providing that all the art, music, sounds, and levels were different (id still holds a copyright on everything included in the IWAD). Regarding Doom source ports, Carmack says:
Any DOOM based EXE would have to have the source available upon request. It doesn't necessarily have to be included, but you have to be able to get at it if you wish. This would prevent a gldoom episode.
There you have it. I am not sure about the status of Doom source ports which use material from other sources. They may fall under the Lesser General Public License, but I'm not quite sure.
The updated Doom source is, naturally, available in our Source Ports section under "Linux," although nothing has changed other than the license information.