I figured it'd be handy to have a thread sharing SRDs and other frameworks to help springboard the game-making process. Here are a few (free) SRDs I'm currently reading and considering.
Passkey, by Penflower Ink. The focus here is that when facing a decision point, a player can either rely on the dice with a luck roll, or choose to succeed by spending a finite resource (Effort Points): the more EP spent, the fewer strings attached to their success. https://penflower-ink.itch.io/passkey-srd
Lumen, by Gila RPGs. Lumen uses d6 pools, weapons, powers, and round-to-round health/energy drops to produce tactical but fast conflicts inspired by video game action shooters. The Lumen games I've seen are a bit more complex than a one-page limitation, but a small make would probably fit. https://gilarpgs.itch.io/lumen
Breathless, by Fari RPGs. In Breathless, stats are associcated to a size of polyhedral die, with roll-high success (5+ is full success, 3-4 is success with complication, 1-2 is failure). Each time you use a stat for a roll, its die ticks down by one size, gradually wearing out your character. You can "catch your breath" at any time to restore your original dice, at the cost of the GM moving in a big way. https://farirpgs.itch.io/breathless-srd
CaltropCore, by titanomachyRPG. CaltropCore features d4 dice pools, with each value on the d4 mapping to a different tier of success/failure. The SRD outlines two different modes of play: stat-driven, where a host of stats will tell you how many d4s to roll; and token-based, where you build a dice pool out of tokens spent to better your odds. https://titanomachyrpg.itch.io/caltropcore
Please feel free to share any other system / game design toolkits you're familiar with!