Design Software?

Does anyone know a free design software that works with unity ?

What do you mean by design software?
What are you trying to design?

hi mwsc i want to design things like characters buildings i dont know things of that nature just for my knowledge so i know how

Blender is the best free 3d modelling software there is.
Well, at least to me it is.

I also want to know more about free design softwares.

there is also shade3d for unity

http://www.mirye.net/shade-3d-for-unity-overview