This is VK/KittenPHP-DB-Engine project, consisting of efficient PHP-to-C++ translator called “KPHP” or “KittenPHP”, and several auxiliary high-performance “engines” (specialized non-relational databases), needed for its deployment.
It has been developed since 2009 mostly by Vkontakte Ltd, operator of social network VK.COM, and thoroughfully tested in high-performance enviroments, until a version useful for the general public was obtained. Fulfilling several previously given public promises, this version is now released for public use under GPL/LGPL terms.
Source code is licensed mostly under GPL version 2 or later.
Benchmarks (KPHP vs Facebook HipHop VM vs PHP):
Tests sources available here.
Russian-language documentation is available at Github.
English documentation not available yet, sorry.