D&D 4th ed, Legend of the Five Rings 1st Ed and 4th ed (but mechanically only as the RP aspect is quite complex), Kobolds ate my babies, Pathfinder Beginner Box. There are probably others but out of all the systems I have played (quite a lot of them when I sit down and think about it) those are the ones that stick out in my mind as the most simple mechanically.
I've heard that some of the d10 and d6 systems are supposed to be very straight forward, but most d20 systems aren't very complicated either. I prefer the D&D 3.5 system, followed closely by the Pathfinder system (aka D&D 3.75); because they facilitate creativity while also giving decent simulation of reality and I find a variety of dice rolls to be more fun, especially for players.
Of all the dnd systems I`ve tried, from 2nd and up, I find 4th to be the smoothest system to dm and the funnest system to build a character. 4e is smooth to run and play, so you have a lot of time to roleplay and not let complicated rules get in your way, havinf to look up unnecessary stuff. I love skill challanges, it can be used for every kind of encounter that is not a pure roleplaying scenario! Just letting the players take the narrative and be creative, the powers they have can suggest what the characters are capable of! That is how I started thinking how easy and simple encounters actually can be done! Even combat can be done like that, if you want to do a more story driven game. But i bet a system like that would be too simple if you still want classes and leveling and all that.
For someone who has never played a RPG and simply wants to learn the basics, "The Marvel Universe RPG":http://en.wikipedia.org/wiki/Marvel_Universe_Roleplaying_Game is so basic that you dont even need dice to play and you can teach it to a six year old without any worry. I use this game system as a training tool for any new role player as it is the simplest game I have ever seen and yet it has the whole background of the marvel universe to work with.
You can literally pick up the game and start play 15 minutes later. No need to read dozens or hundreds of rules. Just get down to business and have fun.
-Steve
"Star Trek Late Night":http://www.obsidianportal.com/campaigns/star-trek-late-night
I think some of the more popular rules light games out there are "Risus":http://www222.pair.com/sjohn/risus.htm and "Microlight D20":http://www.forum.koboldenterprise.com/index.php?action=downloads (an incredibly stripped down D20 system).
Comments
-Jaymes
"Changing History":http://www.obsidianportal.com/campaigns/l5r-changing-history
-Jaymes
Campaign of the Month Febuary 2013
You can literally pick up the game and start play 15 minutes later. No need to read dozens or hundreds of rules. Just get down to business and have fun.
-Steve
"Star Trek Late Night":http://www.obsidianportal.com/campaigns/star-trek-late-night
Cheers,
-Arsheesh