Every PC (Windows/Macintosh/Linux) copy is available in both a DRM-free form and a Steam form. You get both for one pledge.
Sorry, but the physical copies are only available as rewards for the Kickstarter fund-raising project. The game will eventually be made available as a general digital release for the buying public at large, but the physical copies are only a part of the Kickstarter.
By the way, the project successfully raised $176,667. Impressive for a $50,000 goal.