ID, at least while Carmack was there, was very very good about releasing their last-gen engine tech once all licensees had published their games. A whole lot of

ID, at least while Carmack was there, was very very good about releasing their last-gen engine tech once all licensees had published their games. A whole lot of people learned about how to do game development from those things. Unknown Worlds only released the source code for the NS1 mod for Half-Life--and as Valve has yet to release the Gold Src source code, that's of questionable utility.