The "plugin must be GPL" case is highly debatable (I thought this question was solved already ?) If you "work out" the metamod API yourself - read: in practice, use the metamod source code, strip away all that you don't need and rename stuff here and there so that nobody can
prove that you've actually
used it

- you won't be linking against the metamod source code, but just against the HL SDK. And as the GNU people say themselves, a plugin of a GPL program doesn't
need to be GPL unless the author of the main module explicitly wants it so.
And knowing Will Day I can bet that he has chosen to develop metamod under the GPL in order to
give freedom to the coders to look at the source code, and certainly not to
take away from the coders the freedom to disclose theirs or not. But Whistler is a die-hard GPLer, one of those who could turn a license designed for freedom in one of the most restrictive licenses ever. I bet Will Day would have put metamod under the BSD license, if he'd known
