It's not really at a startup stage, but I'm trying to, with some friends and burning man people, see if I can build/design an extremely lightweight and cheap parabolic trough out of carbon fiber and mylar, for electric and mechanical power generation. I'm iterating through to see if wind is a blocking issue.

I also had some designs for a powered wheel with two degrees of freedom, without a caster, to remove some of the angular momentum problems that classic approaches face.