Cimex

Facebook HTML-generation needs seemed to strain PHP capacity to the limit. Since rewriting the whole website was not an option, they wrote HipHop, a PHP to C++ transformer instead: they keep writing PHP code but get a significant speed boost and minimize their memory usage.

HipHop will be open-sourced, given PHP’s ubiquity it will be interesting to see who start using and contributing to this…

FB article: HipHop

Edit: interesting post about one of PHC contributor — another older PHP compiler