The Leopard source code is complete enough to give developers something to work off of when designing an application, but according to Apple's developer mailing list, some users are noting that some key drivers are missing. Apple's forums are rife with pleas for the source code to the iPhone, since its kernel is founded on the same code that currently resides in Leopard. It is unlikely Apple would pursue such a path, having previously blocked attempts at unlocking. Darwin was originally released by Apple in 2000, a combination of NeXT's NEXTSTEP operating system, FreeBSD, as well as code developed by the company.