Hello friend! Not sure exactly what you meant by rules-based, but hopefully there's enough of a variety in the stuff I talk about below that something hits what you're looking for.
Greeve Simulations, by Anrole.
GREEVE: Simulations is a one-shot Forged in the Dark game where players take on the roles of mecha academy cadets in combat simulations.
Play a single round for a quick challenge, or link multiple mock missions together to see how your squad evolvesโor falls apartโunder pressure.
I personally love Forged in the Dark games because of the layers of complexity you can have, depending on the table. The core mechanic is fairly simple: you roll a pool of dice and look for the highest number, and most of the time your roll result will be a mixed bag of outcomes, leading to a natural build-up and release of narrative tension. Players have a lot of resources for how to distribute consequences, whether that be accrueing stress to avoid something you don't want, or leaning on your relationship with other characters to share the load. There's also a lot of tools for the GM to work with: clocks to track so consequences can build up and then land like a pile of bricks, and in this case, there's also something called Scale, which reflects the power differences between characters and their opponents.
Greeve Simulations is a fairly basic introduction to the Forged in the Dark system, but that's good for a group that just wants to engage in a one-and-done kind of game. If your group picks this up and decides they really like the way a session plays, you can play through this game a couple of times and then carry what you've learned to other Forged in the Dark games for higher drama and more consequences to balance.
Boy Problems, by Colin Cummings.
It is many years into the future. A wealthy and powerful person (or persons) has claimed a rare and much sought-after prize: the โvaultโ of 200 unreleased (this is real!) songs from renowned Canadian pop artist, Carly Rae Jepsen.
Hired by an anonymous sponsor, your team of highly trained individuals will raid a well-defended location to retrieve said item. From planning to set-up to execution, you will see this heist through to its completion, whether that be a success or failure. There will many twists and turns along the way, and donโt always trust the specialists by your side.
This one-shot was a hot piece of media a few years ago. It pulls from a simple but satisfying system called **Lasers & Feelings", which gives you a few simple descriptions to determine what sets you apart from your fellow criminals, and a single number that defines your abilities in two different arenas. The game is designed for a ton of drama, double-crossing, and a discography to fuel your imagination.
If you like this game and you want to re-visit it, the creator has two expansions: Boy Problems Side-B, which is full of new jobs and extra rules, and Nocturne of Artifice, which gives you an additional cyber-gothic heist.
Edge Zero Force, by Mundos Infinitos.
Itโs the near future. Only your Special Forces group is capable of resolving its conflicts.
Benjamรญn Anรญbal Reyna, also known as Mundos Infinitos, makes a lot of pamphlet-sized games: great for short sessions that don't require you bring a lot to the table. Edge Zero Force is one of a trilogy of games, the other two being a mech-inspired Armored Battle Frame, and a digital-reality neo-noir Butterfly's Waking.
While these games are compact, they hold a lot. There are mission generation tables, a section for character creation, and rules for tracking resources, using a character tool called Edge, and tracks for your character's Conviction and Guilt - basically an emotional see-saw that either pushes you to character advancement, or takes your Agent out of play.
If you like the rules but you want a different setting, the other options in Reyna's sci-fi trilogy might hit just the right sweet spot.
Aberrant, by Wendigo Workshop.
"You are a monster. An experiment. Your body is smallโฆ weakโฆ uselessโฆ but not for long. You feel it. The potentialโฆ The power.
Animals and monsters were not entertaining anymore, people wanted more teeth. You are the result of these researches."
Aberrant is an exploration/dungeon crawler where you play as an experiment trying to escape the derelict facility within which it was made. Fight the other denizens of The Lab, eat them to grow stronger, and reach the exit to gain your freedom.
I don't think that Aberrant is necessarily strictly one-shot material, especially since mutations and evolution are meant to grow your character's power the longer you play. However, the system it works on, Breathless, creates a tight game loop in which your characters need to take rest actions to replenish their abilities, but each rest action allows for the dangers of the dungeon to catch up. These tight game loops mean that you will likely get through a lot in a single session. Since the game is currently in-development, much of what is out will be enough for a single session, with the pieces that make it re-playable coming out in the future.
Deat Dies Tonight, by NatJones1809.
You lived normal lives, until fear crept in at the edges. You were stalked and tracked and hunted by nightmare manifestations of your worst fears, right up until they coalesced in your homes and ATE YOU.
But death didn't come. Now you're half-monster, souls fused to the fear-demon digesting you, wrestling your nightmare instincts down so you can kill the fear of death and rip your demons apart in the single deathless instant that follows.
DEATH DIES TONIGHT is a one-shot action movie TTRPG for 3-6 players and a GM. Play as once-regular people possessed by archetypal nightmares, use your newfound fear-powers to struggle for your life and kill the Death-Nightmare to free yourself from your terrible fate.
Horror is a great genre for one-shots, because there's a natural end-point at the end of these kinds of movies. Either the horror wins, or you manage to make it out. Like most good one-shots, character creation for this game is fairly quick: you can roll on a couple of tables to figure out who you are. I also appreciate the GM tools available here: you construct details about Death to determine why and how they're a threat, and the PDF comes with small character boxes that you can print and hand out to your players, as well as keep a succinct summary for yourself.
I also like the fact that this game has an outcome where you succeed too well: rolling too high causes your character to become more monstrous, causing harm and fear to the people around them. It works for a horror game!
OMEN is a TTRPG all about defying fate. Designed as a one shot, you and your friends will come together, create a doomed world, and do what you can to save it.
Defy or doom, either way it's a good time.
Designed to be a one-shot, OMEN is a world on a clock: either the world will end, or your Fated characters will manage to defy what feels inevitable. You track both of these possibilities with clocks, which tick towards an epilogue. To try and stop everything from collapsing, the players will have to take on various challenges, using a limited resource from a dice pool.
I think there's definitely some strategy to this game, since you'll have to choose when you want to fail and when you need to succeed. The game is also fairly genre-agnostic: it doesn't matter if the world that's ending is a fantasy or a science-fiction story. Spencer Campbell, the creator behind GILA RPGs, is known for creating tight rules systems that are easy to learn, but can take some time to master: so that makes me think that OMEN might give you a good challenge!
Bugs Against Blight, by Brett Svendsen.
"The Oldgrass is dead, consumed by BLIGHT. The many displaced bugs have followed the RADIANT QUEEN, leader of the Oldgrass bees, to a new home dubbed BUGBERG.
Blight is a wicked substance โ rotting the green, mucking clean water, and turning once kind bugs into irrecognizable murdering monsters.
While little time has passed, Bugberg has become a bustling metropolis. Though little is shared in common amongst these many bugs, they are all bound by common plight.
The Blight comes. Will you let your new homeland fall to the fate of the old? Will you leave your fellow bugs to be consumed by Blight? NO! You are a BUG OF BUGBERG!"
Fans of Hollow Knight will probably really enjoy this Mausritter hack. Your bugs are small and fragile, who get better just by staying alive. This is a great game for folks who like grid-based combat and roll-under mechanics: typically you'll roll a d20 and hope you get a number lower than the attribute you're using.
You'll have to do a little extra work in order to get this to the table, unfortunately: I think you need the original Mausritter rules to play, as the document for Bugs Against Blight is just what you need to make it a conversion about bugs. This style of game also works best with a pre-written dungeon: so if you want a crisp one-shot, might I recommend Sanctum of the Ori Magi, by brstf?
You Can Also Check Outโฆ
My One Shot Tag, where I've cultivated more recommendation posts than I realized!
Tanya Floaker's Games Catalogue has a lot of single-session games that let you wrestle with complex topics.
The Great Soul Train Robbery, by Cloven Pine Games.
Crustacean Bus Station, by Kumada1.
Escape from Dino Island, by Sam Tung & Sam Roberts.
Light Eaters: Thunderfuck, by blindink.
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