yacen
Yet Another Chess ENgine
... library and thus is very portable and easy to compile on almost every platform.
yacen uses the common UCI interface to communicate with any compatible GUI.
NOTE: yacen is currently in pre-alpha status. This means that there is only source code available which is far from complete and thus cannot be compiled to a working binary yet. A more complete source code and first binaries for Linux and Windows will be available when the project reaches alpha status.