Hu-Go is a famous emulator of NEC PC Engine console, running on many system such as Linux and Windows and now Dingux (see http://www.zeograd.com/ for details).
Sources are included, and this package is under the GNU public licence v2, read COPYING.txt file for more information about it.
Many new features have been added compared to original Hu-Go version, have a look to the README for details.