I had what may be an awesome idea. It takes place in an alternate history earth where several key points in history went differently and have severely impacted the future. Why did these events happen differently? Because a gnome (like a garden gnome) invented a time machine and accidentally screwed it all up. Now, it's up to your band on gnomes to use the time machine to go back in time and set events straight. Armed with a history book and your diminutive stature, you have to set history right, for better or worse.
The idea first came to me as an gnome-based RPG. I was trying to come up with a good hook for a gnome RPG and was having trouble. The trouble with such small gnomes is that they aren't disposed to grand, heroic acts because of their size.
Speaking into Joan of Arc's ear to guide her to action.
Ensuring Hitler meets his end.
Being the second gunman.
Acting as Einstein's inspiration.
The gnomes can debate and examine these points in history. If they aren't sure that what they've been sent to do is the right thing, they can look for evidence that maybe it is. They can choose not to do it and see what they outcome is. They get to remold the world from these critical points in time, setting new and different events into motion. Changing history.