Lightweight microgames on a shared Creative Commons core engine. My obsession.
The original, and still some of the best stuff out there by far. $6 (or one of the many free Community Copies) is an absolute steal.
You'll need this if you want to make anything. Also technically doubles as a teeny tiny "core" module to build on top of.
A strong contender for my single favorite 24XX thing: space fighter pilots potentially compromised by war, with the most perfectly-light rules for dogfighting I've ever seen in tabletop. A must-buy.
Reliable, recognizable core for the modular 1400 series of fantasy games. I like the individual games more than the collected PDF; they have weird idiosyncratic takes on Harm and Defense to love.
This dungeon-crawler from the 1400 fantasy series has a delightful variant Harm mechanic I steal for basically all 24XX games + a huge shopping list.
The spellcasting mechanics in this one (where they have a die size of their own that decreases with use or when expended as a defense, restored with proper rest) is impressively elegant, while the 50 spells are a handy bonus.
20 playable fantasy ancestries for any 24XX game you want, masquerading as a game of their own - super useful!
Fantasy heists, with some very fun heist mechanics for players and the GM both - compare/contrast with 2400: The Venusian Job.
Slim fantasy adventure, but with everything you need: people called from their medieval-ish lives to do virtuous quests by the spirits.
On a flooded future Earth, undersea domes struggle to survive and fight for dominance. Players take on the role of crew aboard a customizable submarine; the enormous ocean is their oyster.
Shamelessly Supernatural-inspired fun, with a clever Luck mechanic (it's both health and fuel for certain talents!); lots to like here.
Space Vikings. Those two words will tell you if you want this or not.
Wonderfully off-beat character options for an unnerving premise: exploring lightless worlds, far from any star.
Gothic ghost stories in an era you basically never see represented by tabletop: muskets and chills in a surreal port township...
This generation ship holds vehicle and mech pilots alongside mages and spirits - all presented with satisfying mechanics in a remarkably compact space. Tear these mechanics out for all sorts of science-fantasy settings, honestly!
Reclaim the Earth... or die of hunger and infected wounds, as this handy little toolkit greatly expands out survival mechanics.
A loving love letter to everything good about Vampire: the Masquerade - this casts you as sexy undead monsters in the apocalyptic 1990s <3
Mesopotamian post-apocalyptic survival, clean and inspiring.
Anti-alien resistance with a remarkably versatility of possible settings and invaders. Thank goodness - someone made this, so I don't have to!
Yet another excellent take on heists in a tidy little format, with elegant versions of flashbacks, retroactively-declared gear, and alarms.
Trans-dimensional superbeings traipsing along the timeline to protect humanity from otherworldly threats with simple, cool powers.
A personal friend's killer foray in 24XX: cyberpunk by way of demonic hellfire and power metal, oozing with awesome flavor.
It's Mothership meets Doom in a world where space travel involves a shortcut through Hell... you get a fun variety of characters here!
Meaty (for 24XX, anyway) mecha mechanics for Pacific Rim-style brawls against the enormous monster of the week. Super cool!
Nicely shows just how compact the core of the 24XX engine is. Tuck this into your wallet to stave off boredom after being shipwrecked!
During the day, cheap entertainment draws all sorts of visitors to the colorful tents; after nightfall, it's a surreal race to escape alive! Both halves are realized as mechanically-distinct phases; fun stuff.