Oh my goodness. +Chris McDowall's Into the Odd is the business.
Personal gaming context: I've been thinking up some campaign possibilities for a gaming group. One of the notions I've been playing with is a dungeoncrawl.
The setting for the dungeoncrawl is the modern world. Players can equip themselves with anything you'd find on Amazon, or at Home Depot, or from some weirdo internet swordsmith. The PCs live in a city (I've been thinking I'd make up a forgotten borough of NYC). Of course, the city is sitting on top of a megadungeon.
The gist: There are secret urban spelunking clubs. Most of the wealthy families in town can be traced back to an ancestor who was in a club. The Borough President is intent on stopping the clubs, and closing up any passages to the Underworld that are discovered. The Municipal Sewer Authority is rich and powerful and unruly. The deeper you go, the less technology works, and the more mythic things become. Be nice to the rats, because they can follow you home.
That sounds like it could be fun, right?
And danged if Into the Odd isn' the perfect system for it.
Odd is extraordinarily rules-light. Chargen is four rolls and the actual game mechanics could fit on an index card.
I love rules-light systems, but there is often a sense that they are rules-light by leaving undetermined a lot of important decisions.
Odd, on the other hand, is pared down by focus on a particular style of play: exploration. As such, the game is less concerned with simulating anything (rolls are infrequent and cover broad, abstracted outcomes), and more on creating a tricky, challenging, and memorable scenario for the PCs to investigate.
The results are more old school than the Old School. Lots of things happen automatically in order to focus attention of player choice and player skill instead of mechanics. Combat strikes always hit, although damage is highly variable. Monsters reliably wreak havoc. Any adventurer can break down any door or pick any lock, given enough time (but they won't always have enough time, and there's the chance of attracting unwanted attention, or setting off a trap). Traps are almost always detected, because working your way around a trap is more fun than being told you're surprise-dead. Death is common, and you are advised to value expediency over realism in getting a replacement character into the party.
Time and time again, while reading the rules, I'd nod and think "Yes, of course." Everything is so danged playable. These are clearly battle-forged rules, honed and practical. Odd is elegant not for elegancy's sake, but because only the fittest rules have survived.
There's not a magic system, but there are magic items, and you have a decent chance of starting out with one. This would make it a poor fit for some campaigns, but is exactly perfect for the one I have in mind.
Rather than go into more detail, I'll just point you at this free pdf that covers the player-facing rules.
Now I face the task of digging through Mr. McDowall's blog, SoogaGames, which is packed to the gills with really useful game content. F'risntance:
How I Run Into the Odd—good advice for any GM.
Odd Classes and Orders
3HP, Sword (d6)—from one stat line, many NPCs.
Jolly Underground Ghost Cruise with Severin Sistern—a no-prep adventure.
The full game is available via Lost Pages. Highly recommended.