Minions is quite unique - it can be played standalone, in which case it forms a sort of narrative storytelling system, or it can be "bolted on" to any other generic rules mechanics and played as a sort of setting-cum-scenario. The rules mention FUDGE as being especially suitable for mechanics.
Minions is set in an urban area--time-period irrelevant. Thus, a medieval fantasy city, a modern metropolis, or a futuristic space station would all work fine. There just have to be a lot of people concentrated in one place. The game involves generating thirty-two characters very quickly, so obviously FUDGE or similar systems with very streamlined mechanics are highly preferable to other rules-heavy systems. These characters are more like "non-player characters" in traditional RPGs than typical "characters"--they may (and do) change players during the game.
The game is played by attempting to weave together the narratives of multiple characters so they become inextricably involved in a single "faction" which forms a support base for the urban area operations. Atypically, the roleplaying game results in a winner when one player assembles the largest faction and all characters are aligned with a faction.
The rules of minion deal with characters, characterization (brief), and changing loyalties and how this occurs. These rules may stand alone or, as mentioned, by integrated with any other universal mechanics.