Thrawn's Revenge is a large-scale mod for Empire at War: Forces of Corruption. It includes the events of the Galactic Civil War after Palpatine's death at Endor, up until the signing of the Pellaeon-Gavrisom treaty. If you own the Steam version of EaW, you will have to complete extra steps to run the mod after installation. Please see the manual for these steps.
Although mentioned in a few places, the Beta class was never given a proper depiction in any Star Wars media, so Valeria has given it a new design as part of the upcoming Hapan playable faction.
Top notch concept art, looks pro!
Seems like Hapans really like General Grievous. :P