The engines and SRD I typically draw inspiration from for my hacks are: Lasers & Feelings, Push SRD,  Schema, and Second Guess.

Other games/systems I'm more or less familiar with: Action Castle IV, Apocalypse World, Blades in the Dark, City of Mist, Crescent Moon, Dungeons & Dragons 5e, Golden Sky Stories, Honey Heist, Inspectres, Kids on Bikes & Cia., Libreté, Lumen, Monster of the Week, Monsterheats 2, Monsters and Other Childish Things, Mouse Guard, Mouseritter, Query Six, Quest, ROOT, Ryuutama, Slugblaster, Tales from the Loop & Cia., Threadbare, and Tiny Dungeon 2e.

Besides the stuff on my Wishlist, the engines and SRD I want to check out are Breathless SRD, Carta, Charge SRD, Caltrop Core, CORE Micro, Four Points, Freeform Ultimate, Hopes & Dreams SRD, The Pool, Tiny D6, and Wretched & Alone SRD.

Other systems that I also still haven't checked include 2D20 SRD, 4D4S SRD, Belonging Outside Belonging, Cairn SRD, d20PFSRD, Death in Space, Dice Goblin SRD, Drama System SRD, Guided by the Sun SRD, Harmony Drive, Into the Odd SRD, Lost & Found, Miso, Motif OGL, OpenD6 OGL, Paragon, Personae, Pit Drive, Quest Worlds, Simple World, Spirals, Starjammer SRD, Stars Without Number, The House Doesn’t Always Win, Troika!, VIIN, and all of these!