"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)."
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