Unexpected, but here it is.
What follows is a list of RPGs which, in my limited and human judgment, are frequently used as (or maybe just recommended as) rules toolkits: i.e., the mechanics are used or tweaked to run games in genres or settings other than those presented in the rulebook. For some games, like GURPS, that’s sort of a gimmie.
If you like a system, but you just use it for the setting(s) it was written for, italicize it. If you like a system and it’s one of your go-to tools for running games in random settings, bold it. If you like the game world but don’t care much about the system, leave it alone — you wanna identify the systems that you can practically teach from memory.
Copy to your own blog and repeat as desired. If there’s a game you’d bold that isn’t listed, add it. (I like Unknown Armies a ton, but it’s not one of my generic systems, so I wouldn’t add it.)
Big Eyes, Small Mouth (and variants)
Chaosium Basic Role-Playing (Call of Cthulhu, RuneQuest)
Cinematic Unisystem (Buffy, Angel)
D&D 3rd edition (3.5, any D20 variant)
D&D 4th edition
D6 (Star Wars WEG)
Dogs in the Vineyard
FUDGE (or FATE)
Legend of the Five Rings (and variants)
My Life With Master
One-Roll Engine (Reign, Godlike)
Over the Edge
PDQ (Dead Inside, Zorceror of Zo)
Storyteller (any version; Vampire, Adventure, Exalted, etc.)
The Fantasy Trip
Traveller (1st edition)