Oh yeah, there's definitely concerns in general. It's not as easy for shippers of proprietary software as say the BSD license, you've got to keep a clear interf

Oh yeah, there's definitely concerns in general. It's not as easy for shippers of proprietary software as say the BSD license, you've got to keep a clear interface separation between your proprietary code and the GPL code etc. You might also have lawyers who are lazy about it and don't want to deal with the liability, "we heard Apple banned GPL code..." or "the FSF sued Cisco...". But there's no license reason for why you can't use that GPL code in some way, and everyone from Google with Android to Oracle with Oracle Linux and their DB bundles GPL code that's directly used by some accompanying proprietary piece of software. But what I was more going for is that there's also a non-legal aspects to it that go beyond the license, which is that some maintainers of free software are actively hostile to their software being used as a smaller component in some proprietary product. The GCC project is probably the most famous example of this, I think this has changed somewhat in recent years with LLVM+Clang, but they used to jealously guard things like their AST format. So e.g. someone with a proprietary editor (or Emacs for that matter...) could never hope to use GCC for spewing out parsing information for some C code. I think it's fair to say that the Git project isn't like that. If someone maintaining proprietary software needs some plumbing interface to hook their stuff up and is willing to submit patches it'll be received as well as any other change (subject to review, maintenance & backwards-compatibility concerns etc.). If they find it useful it's likely that other people will too...