Some of my favourite games were d% and came from Chaosium (RuneQuest, Ringworld, Call of Cthulhu, AND the rules-system was licensed to OTHER SUNS by Fantasy Games Unlimited) and the generic foundation is Basic RolePlaying , which is now an extensive 500-page book with "fingers" into each of the genres Chaosium previously covered. It is also available in a Quick-Start edition for cheaper. <a href="http://catalog.chaosium.com/index.php?cPath=37" rel="nofollow">http://catalog.chaosium.com/index.php?cPath=37</a> The system proposes some basic 3d6-based characteristics but then a large list of skills. For some skills you definitely need specialized education, such as the sciences, so any unskilled character has a base percentage of only 0% or 1%. If it is a skill that is more intuitive and can be done somewhat by even an unskilled character, they give the skill a bigger "floor" like 10% or 20%. In some games, having high characteristics gives you a bonus to base% for some skills. Characters develop their skills by checking a box that they have used the skill in the current campaign, but they only get an increase if they can learn something new. That is achieved by having to roll OVER your current skill-level, which gets harder and harder. If you succeed, get 1d6 more percent in the skill. This is a good advancement system. Percentages above 100% are possible. This must be in conjunction with a critical hit system: rolling 1/20th of the roll you needed or less is a Critical Success, rolling 1/5th of the roll you needed or less is a Special Success, and rolling in the top 1/20th of the range of percentages which are failed rolls is a Critical Failure aka a Fumble. Having skill-levels over 100% will mean you can basically always succeed at normal tasks, except you can still fail or fumble, but give you more beneficial Criticals and Specials more often. RuneQuest had an extensive table of Fumbles, based on what the Society for Creative Anachronism experiences: armor-straps break, swords slip. The "Murphy's Rules" column of SPACE GAMER joked that, if you applied the rules exactingly, out of a large army of 20,000, every round of a pitched battle something like 5 soldiers would disembowel themselves and 2 would cut their own heads off! My MOST favourite system is STAR FRONTIERS: Alpha Dawn (1982, TSR). It had a very restricted set of only 13 skills in the basic game, but many sub-skills within each skill, with a base% chance + 10% added per Level in a skill (in the basic game, skills were Level 1-6). In that way, with different base% chances, easy and more difficult sub-skills within a skill (like computer programming vs. difficult hacking) would be defined and give different percentage chances for the same level of the skill. Trying to use alien weaponry or tech was -20% though! In an age where now all kinds of esoteric RPG dice-rolls are used, I still consider this the best for fast-and-furious combat rolls for melee, ranged, vehicle and aerial vehicle combat all in the same six-second-turn framework. But since it was still d%, you always had a feel for what your chances were and could switch approaches if you felt your character's chances were too low. You can download the current, fan-edited edition here for FREE (and tons more stuff like the expansion sets, many of the old adventure modules, and a colourful fan magazine), or buy the hardcopy versions at print-cost from lulu.com . The fans originally secured a deal with TSR that this stuff would be available as long as no one makes a profit from it. Originally this game was meant to be mass-marketed and sold in far-flung bookstores, and land with suburban teens who might never have heard of RPGs or been in a group, so they explained running RPGs and designing adventures VERY well. RUN, don't walk over and download it. <a href="http://www.starfrontiersman.com/downloads/remastered" rel="nofollow">http://www.starfrontiersman.com/downloads/remastered</a>