Apple Public Source License (APSL)
The license Apple wrote in 1999 to release Darwin, the open foundation underneath Mac OS X.
Version 1.0 drew sharp criticism from the Free Software Foundation. It required modifications to be published even when they were only used internally, let Apple terminate the license, and so failed the FSF's definition of free software. Apple revised the text several times, and APSL 2.0 in 2003 was accepted as free, though its weak copyleft can't be combined with the GPL.
The APSL still covers parts of Apple's open components, including the xnu kernel. Nobody outside Apple picks it for their own project; it exists so that a single company can open code on its own terms.