From the author's page:
"Microlite74, like its parent game, Microlite20, is a trimmed-down, sub-miniature version of the Primary Fantasy SRD rules that has been designed to be quick and easy to play. The goal of Microlite74, however, is to recreate the style and feel of that very first ("0e") fantasy roleplaying game published back in 1974. If you are at all familiar with any game based on the 3.5 edition of the Primary Fantasy SRD, you will find Microlite74 easy to play and easy to run as a GM, but with an extra helping of "old school" flavor.
While Microlite74 is designed as an introduction to "old school" play for players more familiar with modern rules systems based on the Primary Fantasy SRD, it is a rules-lite OGL based game system that old school grognards – especially those who cut their gamer teeth on "0e" – should find equally enjoyable. It is also easy to modify with your own house rules or rules drawn from your favorite edition of the world’s most popular fantasy roleplaying game."
Oddly enough I do not care for most open rule sets, even though I am hypocritical enough to write my own. I think they are mostly just a book of glorified house-rules done for self indulgence. Other people obviously think otherwise as it seems many of these open systems are becoming fairly popular. Anyhow, this compilation of rules hit a cord with me, mostly because of the brevity it illustrated with spells, monsters, and the like. It is interesting how minimal you can go and still have it very recognizable as D&D.