Zaero is an unofficial add-on to Quake II. The Strogg seemed to be defeated but now they are back. You are part of the elite fighter squadron Zaero and it's your task to battle the new Strogg Rebellion using 9 all-new weapons and various new special items. Zaero includes 14 levels and a large number of new enemies.
A nearly-exact copy of the retail game can now be downloaded from the Team Evolve's website. Although the filename and the links on the site suggests that this release is still a demo - it is; in fact, a cropped-down version of the original game. It features all 14 SP maps, though lacks the intro / outro cinematics and the new textures that give the add-on pack a unique-look.