YS Belkan War Edition (YSBWE) is a conversion of the (now-obsolete) 2007 version of YSFlight based around aircraft and locations featured in the Ace Combat universe, primarily AC Zero. The GAC-based aircraft and map used by YSBWE have been released separately here on HQ before, but until now, the game itself has been effectively lost. The archived copy linked here was found by Scarecrow in 2014, and now rediscovered again on my old hard drive.
YSBWE features none of the stock aircraft or scenery of a normal YSFlight build. Instead, it uses a single large map with different IFF regions, and a wide selection of GAC aircraft derived from Ace Combat Zero. Based on this setup, it can be assumed that this version of YS was once used to host a specialized WW3-like server.