From publisher blurb:
Microlite78 First Edition Lite is a trimmed-down miniature version of the Primary Fantasy SRD rules designed to be quick and easy to play, especially when compared to modern incarnations of the game. The goal of Microlite78 First Edition Lite is do for First Edition (1e) what Microlite74 did for the Original Edition (0e): to recreate the style and feel of the First Edition of the world’s most popular fantasy roleplaying game published back in 1978 without giving up all of the clearer mechanics of modern D20-based versions.
The Microlite78 First Edition Lite rules are based on the Microlite74 Extended rules modified as necessary to fit the 1978 First Edition (1e) of the world’s most popular fantasy roleplaying game. Modifications include detailed first edition class descriptions with a standard old school experience system (instead of one based on Microlite20); complete monsters, spell, and treasure descriptions; rules for strongholds, magic reasearch, optional psionics, and more. These rules are not intended to be a clone of the first edition rules, but rather a conversion of them to a rules-lite D20-based system that encourages old school play without strictly old-school rules. Although Microlite78 First Edition Lite is a complete game, it assumes a basic knowledge on the part of the GM of how roleplaying games and the basic D20-system work. At about 160 pages, the rules are lean and do not hold your hand.
Microlite78 First Edition Lite can easily be used with all original first edition adventures and settings (as well as those for BECMI or second edition with a bit of work) as well as with modern OSR adventures and settings.