Hero System (Champions! c1981 through HSR/BBB c1989-99 & FRED was OK, too)
1) Effects-based universal point-buy system. You can build any character, monster, gizmo, power, cool move, hazard, or, heck, plot point, from any medium or genre, based simply on what it actually /does/, not it's press releases, not what it "is" or how it does it, just the actual 'effect' it accomplishes in the story. Then you just describe all that other fun stuff how you like. You can even create the system artifacts that make other systems 'unique.' Want your plate mail to deflect hits but offer no actual protection, even though that's not what "armor" does in Hero? No problem: +8 DCV, OIF

latemail.
2) Geometric scaling, including the Time, and (a stretch, perhaps) Speed charts. The Speed chart is a way of letting some characters be a lot faster than others, while still letting them all participate reasonably in the same fight. The Time chart was a roughly geometric progression that you could walk a 'power' or modifier up or down to get a value for things like a casting or warm-up time or a fixed duration or a rate of travel for your interstellar drive or what-have you. And, the in-story magnitude of any weapon/ability/superpower/whatever scaled geometrically as the mechanical points invested in it progressed linearly (typically by steps of 5pts, but not always) - which, surprisingly, is not that 'unrealistic'(a .44 is deadlier than a .22, but it's not strictly 8x as deadly, even though it has 8x the kinetic energy) - which enabled playing a team with wildly different power-levels, without making most of them useless compared to the one heavy-hitter.
3) Cost Breaks: The build system would not have held together without secondary characteristics and power frameworks that allowed a character to be somewhat rounded and still viable. Without them, the point-buy system could have incentivized extremes - glass cannons and teeny hammers and the like - too much. And without Disadvantages and limitations to give characters and their abilities weaknesses, drawbacks, and genre caveats.