Wondlan has introduced a new motorized video camera slider, but instead of the typical pulley belt system, they are using a direct gear drive method. The geared motor is built inside of the trolley and meshes directly to a rail that runs along side of the slider.

Doesn't quite mention if it can be used as a basic manual slider in case noise may be an issue. Minimun speed: about 0.555 cm/s and Maximum Speed: about 15 cm/s. It's probably directed more for simple video movements as this product does not include an advanced motion controller that can trigger your camera's shutter or to offer shoot-move-shoot (Interleave) for Time-lapse photography. Check out the product via eBay (click here)

Wondlan Geared Motorized DSLR Video Slider

If you're looking for a more advanced Time-lapse slider, not just simple motion control, there is the Konova Smart Controller (here) and also the Dynamic Perception Stage One (here).