From the Back Cover:
Microlite74 games are trimmed-down miniature versions 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 Microlite74games is to recreate the style and feel of that very first ("0e") fantasy roleplaying game published back in 1974 without giving up all of the clearer mechanics of modern D20-based versions.
The Microlite74 Basic rules are based on three little booklets found in the boxed set of the 1974 original edition of the world's most popular tabletop fantasy roleplaying game. The rules are not intended to be a clone of the 0e rules, but rather a conversion of them to a rules-lite D20-based system that encourages old-school play without strictly old-school rules. Microlite74 Basic is the third edition of the original Microlite74 rules.
Although the Microlite74 Basic rules are complete, they are fairly basic. There are only three classes (Fighters, Magic-Users, and Clerics). Spells are limited and levels top out at 12 to 14. Microlite74 Standard includes many more classes and spells - all over those included in the original edition and its supplements. Microlite74 Extended includes all the material in the standard version extended with a number of house rules the author used in his 0e campaigns starting in the late 1970s. Microlite74 Companion volumes add even more options to the game.
These rules assume that the GM understands the basic concepts of roleplaying games, but provides information for both the GM and the players on the various "old school" styles of play. Microlite74 games can easily use adventures and material from early editions of the world's most popular tabletop fantasy roleplaying game or modern clones.