Old School Hack, Basic Version (2011)

Publisher's blurb & user summary:

Old School Hack is a table-top roleplaying system that's a hack of a hack of the original Red Box version of a certain popular hack-and-slash fantasy game. That's a lot of hacking.

Old School Hack is a hack inspired by Basic D&D, Storming the Wizard's Tower, Lady Blackbird, and most notably Red Box Hack.

Red Box Hack in turn is a sort of a reimagining of Basic D&D, only with some story-game elements and set in a more wuxia asian-themed world. Like D&D it has levels, hit points, and classes, and XP is gained through killing monsters and getting treasure. It's simplified quite a bit, and is extremely and entertainingly pick-up-and-playable.

You can download the complete text of the game here: Old School Hack Downloads, which includes character sheets and conflict cards.