[pcwalton]

Like the other projects mentioned, LLVM was open source before Apple starting leading its development.

[anoncowherd]

.. But you can be sure that Apple's contributions have taken it far further than it would otherwise be.

[rsynnott]

But _clang_ wasn't; it didn't exist. Clang isn't just another name for LLVM or something; it's a compiler using LLVM.