Valve have released the latest small update to Team Fortress 2. Following on from the update released at the start of May, it's another that pulls in some community-provided fixes thanks to the source code being available as part of the Source SDK update.
What? The two things have nothing to do with each other. A GNU operating system doesn’t need to be open source or have its source code available anywhere. A GNU operating system just means it uses GNU tools.
You could write a new kernel from scratch, never distribute a single character of the source code, make an operating system with your new kernel along with GNU tools, and even sell your operating system, which the GPL allows for. The GNU tools would still be open source, sure, but your operating system would be neither open source, nor have its source code completely available.