The same was true for their Angel & Buffy games. Which makes sense since they essentially use the same system. Angel in particular had a set of demon creation rules you could use to make almost any type of monster you wanted to make. It was also easy to adapt a lot of different character types from various genres with the character generation rules. Man, what happened to Eden Studios?
Not just
BTVS and
Angel - but also
Army of Darkness and
Ghosts of Albion. 4 games, 1 system...
And for those unfamiliar, Eden Studios pushed two game systems...
The four I listed above are Unisystem Light, aka "Cinematic Unisystem" - which is player facing rolls, and uses only 1d10 per player, damage by weapon and use action and margin of success...
And Unisystem, aka "Original Unisystem," "full Unisystem," or "Unisystem Heavy," Including
All Flesh Must Be Eaten,
Terra Primate,
Witchcraft ... uses mostly d10's, but also needs a standard poly set for damages, and is mostly opposed rolls. There are more full unisystem games, but I'm not certain on which.
I don't know which version City of Heroes used.
Note that AFMBE, BTVS, Angel, AoD, GoA, TP, and Witchcraft are all still available on DTRPG. Apparently, Fox was very generous about PDFs being "remaining stock" as long as the per-copy royalty checks clear.
Oh, and there's an adaptation of BTVS to do a space cowboys setting... in one of the "Eden Studios Presents" volumes... it's clearly intended to be Firefly, but it would work just as well for a gritty version of Cowboy Bebop. (Makes me wonder, which Spike would win if the two faced off...)