One of those posts that's so nerdy I'm almost embarrassed to put it up.
I was looking for something to replace or at least spice up Sofia & my Warhammer Quest games (getting bored of fighting the same orcs & minotaurs over and over) and seem to have hit upon it. I was looking for something both simple enough for a 5 year old and DMless. Although Sofia and I used to play a diet Universalis when she was younger she stopped liking it, but googling around I seem to have discovered close to the perfect solution: Mythic.
Although the rulebook is pretty long (and it has some lame cheesecakeish artwork) the core rules really could be boiled down to: ask yes/no questions and roll on a table. Someone into tactical or power gaming (wait, that's usually me) wouldn't be satisfied--in fact, I was really skeptical that it would work--but for collaborative storytelling where each of us gets to "be" a character, and we can play in any genre we want (it ended up being Last Airbender fan fiction, but that's ok), and play fast, it was great. After dinner and before bedtime we beat the giant spider, rescued the avatar and his companions from its webs, and saved an earthbender town from a fire nation sniper. Sofi's character ended up badly burned and Saka's still missing - a hook for a later game session. We used some of the maps and minis from other games, including WHQ, just for show and tell. I have to admit I mostly drove (I'd keep asking Sofi, "What do you think should happen now?" "I don't know! I have no idea!") but occasionally she stepped up (Jamie: "How many fire nation soldiers should there be? An army? A squad?" Sofia: "ONE! Just one!" ...she found the exploit...)
Afterwards I was, of course, tempted to "improve" the rules - I hate tables and if I can find some cool system of die-rolling against a threshold or opposed roll to get away from using a table then I'm usually much happier. (When Sofi & I play WHQ it's modded so I don't have to look at the creature's stat cards all the time.) But after dicking around with some experiments I decided I was wasting my time - it's just one table, after all, which one can keep a printout of handy...and would a different die-rolling system really make it any more fun?