For the most part, the game's core is Lamentations of the Flame Princess as written, including the magic system wholesale. We did decide to toss out the Vancian "spell per level per day" setup in favor of a mana-pool based system, however.
The biggest departure is rewriting the classes and races in a fashion that mimics AD&D, with the races breaking down to: dwarf, elf, half-elf, half-orc, human, and wildling - the lattermost being a custom race that takes the place of halflings and gnomes both. Current classes include:
Warriors: Barbarian, Fighter, Paladin, RangerClerics and Mages are fluffed in a somewhat sword-and-sorcery fashion that neither confirms nor denies the existence of gods, with clerics gaining their powers through gnostic mystic shenanigans. All classes advance in AB and we use ascending AC. Certain classes have been buffed from their common AD&D setup, and the Shaman and Brawler classes have been created whole-cloth (replacing Druids and Monks, respectively). Weapons and armor have been slightly rebalanced as well.
Magic-Users: Cleric, Mage, Shaman
Rogues: Assassin, Bard, Brawler, and Thief.
The most obvious LotFP import is taking advantage of the d6 system that Lamentations uses for "common activities," and certain classes have been mechanically written to either gain advances in specific tasks, or gain points in the same fashion that Specialists do in LotFP that they may spend on specific tasks.
|Digital Edition Meatgrinder Character Sheet|
So far, it's working extremely well. The system is very easy to run and adjudicate, and as I invest more time and energy into the campaign (run very West Marches style), I'm adding more random tables and other fun nonsense so that my job is 90% rolling with their punches and interpreting results. The players seem to be having a blast as well. It's been a very refreshing experience.