I'm about to tell you about my high-tech chore system.
Isn't it pretty?
Basically, I assign them a couple of areas that they are in charge of for the whole week. When it's time to pick up, every one cleans their area. It doesn't matter who messed it up. If someone's job is overwhelming, then I assign him a helper. Although, usually it's best for them to work alone. When they try to work together, it often turns into a fight about who's doing all the work and who's not.
That's it. There's nothing magic, but for right now, it's working. And it gets the house cleaned pretty quickly. We clean about 2-3 times per day. To be perfectly honest, the house is not picked up most of the time. We spend a lot of the day at home. And while I home school the bigger kids, the little kids make a huge mess. I would rather deal with the mess than have my kids in front of the tv or some other form of media. Or that's what I tell myself when Jopie and Cry Cry pull all the pillows off every bed in the house and build a huge fort in the living room. Or when I go in the playroom and it they've dumped several bins on the floor, so they can "find something."
I'm sure I'll have a different system when this one wears out. But for right now this is simple, requires no maintenance, and works well for us.
What works for you?