it is Windows 2000 with more added API's in dll's , in the level of compatibility of App's Windows 2000 and XP are very similar , Windows 2000 can execute any app can Windows XP work on it as mypall 68 , teamviewr 14 , 360 Extreme Explorer , the latest vlc version , Firefox 52 and maybe 54 , and more and more new app's can run on XP and vista.
Ximonite started to create an newer extended kernel starting from wildbill rewrited kernel32, if this project successfully completed Windows 2000 it was more compatible than XP and it was same as vista and 7 , look this : https://forum.eclectic4un.me/viewtopic.php?f=25&t=51