A few months ago, I ran a totally free-form game for Matt, Brian, Sara and Maddy. Jeanne was out of town at her mom's and I wanted to game.
I made up a super-simple system with about three attributes, five skills and one resolution table. You always roll 2d6 for challenges. Damage was 1 to 3d6.
Simple and fun.
Here are some of the pictures from the dungeon adventure I made up on the spot. I just kept grabbing cool minis out of my MageKnight boxes (no, I don't play MageKnight -- I bought them in huge lots for use with DnD or Savage Worlds 0r Fate -- any RPG).
It was a fun night and I think everyone enjoyed it.
Enjoy the pics!