Do you know hydraulic cylinders (aka hydraulic motors) ?
Well, this slideshow is about an electric "counterpart" prototype, which use a DC motor, a bolt & nut, and an aluminium cylinder.
There is no casing, and no mean to prevent the cylinder from rotating yet ... but that's just a prototype ...
PS : thanks to Gmoon and Proteus who told me how it was actually called in English. =o)