There has been a very positive trend in RPG design these past few years where folks are taking Open Game License rule systems, breaking them down to their most essential components and re-releasing them as 'microlite' games. I am guessing the term microlite originated with Microlite20, which is the d20 system parred down with laser precision to its most basic elements, and it does so without loosing the flavor of the game. (I am sure there is a lite beer joke waiting here, but I am walking away from it right now) My favorite version is Microlite20 Purest Essence, designed by Robin V. Stacey, Darrell King and Al Krombach.
Actually, it seems there are several variations on the microlite theme for d20. Randall Stukey from RetroRoleplaying has been hard at work developing Microlite74, Microlite75 (published as two books: Characters & Magic and Options & Monsters), as well as an upcoming Microlite20 OSS (Old School Style) and Advanced Microlite20 OSS. He has been a busy guy!
Another busy guy is James D. Hargrove, who has a couple of microlite style games under his belt, those being Core Elements and Simple 20. Butch Curry of Zombie Nirvana Games has released a 'toolbox' edition of Core Elements, though ZNG seems to be down at the moment, but keep an eye on it and make sure to download Core Elements as soon as it comes back up.
Another microlite game that is out (this one is not based on the d20 system) is Mini Six, which takes OpenD6 and boils it down to less than 38 pages of solid gaming goodness. Mini Six is published by AntiPaladin Games and is written/designed by Ray Nolan and Phil Morris. For those of us who are longtime fans of the D6 system, Mini Six comes to us as more than a small miracle, with the kerfuffle that seemed to plague West End Games there at the end, and the way D6 was mishandled these past few years.
I am sure there are many more of these types of games that I am not aware of. I know each of these games has a rabid following, though some are more popular than others. All of the games mentioned in this post are free to download, and some are available to buy in print. As a gamer who prefers rules-lite systems, I am a big fan of them all, and admire all of the designers who have worked so hard to bring them to us. And doing so without a hefty price tag attached! These games are highly playable and prove that the number of rules padding a system does not necessarily make for a great game...