If you are looking for a quick and easy-to-learn, fast paced and fun RPG, look no further than the Mini Six System by Anti-Paladin Games. I was, and downloaded Mini Six and have never regretted it.
Mini Six uses six sided dice only, and allows for complete customization of your characters within the genre or setting you create. No classes that require a player character to rigidly adhere to only certain skills; players can create their own unique characters, using the Attributes and Skills system. The Perks and Disadvantages in character creation permit you to give your characters fun quirks that can improve game play or simply give your character even more personality.
Mini Six offers two systems of combat, one more fast paced than the other. Having tried both, the old D & D gamer in me felt more at home to the static-stat based combat system, but the point is you have options.
Finally, the Mini Six handbook comes with 6 sample settings, all of which are easily playable as is, and with a little tweaking can be even better. And the game is easily customizable to any setting and any genre without a lot of blood, sweat or tears on the part of the GM.
There are some downsides to the game system. The magic system doesn't scale well, and the experience rewards can, over time, make characters far too powerful too quickly. As the NPCs in the handbook do not scale up from their most basic template, that means either a mid- to higher level character will simply walk through their enemies in combat, or the GM has to spend some time scaling up the bad guys to give theri players a challenge. Mini Six is also most definitely NOT a complex game, so for players and GMs who want more complexity in their RPGs, this might not be the game for you.
The downsides, however, do not detract much from the game, in my opinion, and several people, including the publishers have addressed the limitations of the system with possible fixes that gamers can add to the system. For what it is, a univesal role playing system, it does eveything it advertises. Plus, you will never beat the price of FREE. I heartily recommend trying Mini Six, especially if you have always had that fun one-shot idea for an adventure, but never had the right system to play it with. Now you do!