Θ Games: Roleplaying: Genres: Universal: Free

Site list:

ARM Minimalist system using logarithmic scales for all game mechanics.
Oroborus multi-genre RPG Rules light, point allocation, skill based game from Ragnarok Press.
DCS A simple role-playing engine, which can be customised for various game worlds and game types.
GURPS Lite Free 32 page PDF version of the GURPS rules. "Covers the essentials of character creation, combat, success rolls, magic, adventuring, and game mastering."
Gestalt - Innovative Roleplaying Web Site of the Gestalt Roleplaying System. Featuring system rules and scenarios for free download. "Coming soon".
Hyper Generic role-playing game. Official site.
Storytelling20 A "storytelling-oriented" game with rules available in English and Italian.
The Window Flexible, modular rules built around three gaming precepts.
RIP Diceless system. Includes sample dark future and fantasy campaigns.
The Guide to Adventure Includes fantasy and science fiction campaign settings.
EGO-Endless Gaming Options A simple, universal system, with a stable core rule, a complete foundation, and plenty of room for modifications. Free to all.
Ex Mortis V 1.0 BRPS Ex Mortis base role playing system. Free to the public. Fully functional RPG.
Quasar Role-Playing Game Public domain rules intended for family-friendly roleplaying.
The Osprey Open Source Roleplaying Engine A point-based, skill-based roleplaying game distributed under an Open Content license.
GAME Skill- and attribute-based rules designed to fit on one page.
The Awakenings Rules Engine TARE, a universal rules engine. The complete basic rules are currently free, with two commercial campaign settings available for it.
The Ladder A generic rules-lite roleplaying game that utilises neat little character descriptions and a five-rung ladder of task results as the core mechanic.
Shadows Simple yet powerful roleplaying for all ages.
Epitome - Continuous Roleplaying Game Freeform organic diceless system that puts system mechanics in the hands of the users.
SAGA A small system using attribute based dice pools.
POLY, a free, customizable system for table top and LARP A modular system that is adaptable to many styles of play.
Generic Roleplaying All Purpose Engine A free, one page, generic game system.
Alternate Realities A free universal RPG by Carter Butts, Karim Nassar, and Brian Rayburn. Approx. 88 pages (HTML, MS Word, Postscript).
3Muse D6 RPG System Free multigenere RPG system. Currently has fantasy and SuperHeroe rules.
Harpe The Hugely Adaptable (Action/Anime) Role-Playing Engine is a free, easy to use universal role-playing game geared towards high-action/anime role-players, but can be used with any RPG style and genre.
Nuelow Series of interlocking games that focus a little more on love (both in the ideal and carnal sense) than those that have proceeded it.
Percentile Dice Game System A 2 ten sided dice using system released under the Free Gaming License.
DUDE Role-Playing Game This diceless universal determination engine is a one-stat, cinematic, freeform RPG, with several sourcebooks.
Infinite Horizons Freely available rules for a multi-genre role-playing game and supplements.
Paradox A multi-genre system. Basic and Advanced rule books are available free for download.
Role Playing System Foundations for a game system, reference implementation of that system and resource page to develop game worlds.
Alpha-Zulu Games Contains to free games: Alternacy, featuring character-driven skill development; and Mnemonic, a minimal rules, memorizable system designed for portability.
Campaign HQ By Craig Griswold. Contains scenarios, rules, and paper minis.
Draft RPG A small set of rules suitable for running compaigns of independent backgrounds. Open content license, downloadable in PDF format.
Dramats Personae Free simple role-playing system; there are no statistics, little math, no complex charts of equipment, and no magic. Characters represent skilled, but human (or roughly human), beings and have to use their wits rather than their powers, attributes or magic items to succeed.
Hexatome: Exploiting the Number of Six Light-weight role playing game rule system which emphasizes simplicity as well as the scenario and fluently progressing plots.
Impresa Modular Roleplaying System Modular RPG construction set. Free express rules for download include open collaborative license.
Kaleidoscope RPG Support Page An open ended system that adapts to a range of settings and genres with few rules.
OPIGS Supers One page gaming system for super heroes.
OPIGS: Simple one page gaming system.
Fantastic Realities Works with any time period and genre, includes 16 species, magic and monster systems, and realistic rules all of which are optional.
Universal Features a free, universal roleplaying game system. Also includes supplements for the fantasy and Doctor Who genres.
Simple Rules Engine A two page generic skill and attribute based roleplaying engine, focused on characters and stories.
ToAd A model reality kit, where what seems real is real.