I'm thinking about game concepts, and there's one that I've been working on for a while.
The game idea is for a starship game, where players get to command warships in battle, shooting at each other. It's how I think starship combat should be-ships shooting at each other at massive distances, not Star Trek "I can touch your hull!" combat. Torpeoes flying across the sky, right behind them is a storm of missile fire, as warships burn across the night.
There's another one that I'm working on, think of it as X-Com with giant robots. You build the robots, build up bases, and try and defend San Francisco (the sequel will be in Tokyo...).