The Kessler Cineslider is a heavy duty portable linear slider system.

From Kessler:

The Kessler CineSlider is a robust, yet portable camera slider for rigs weighing up to 80 lbs. The CineSlider is a very portable solution to get quick and smooth dolly movements without having to transport a large dolly system. Best known for its drag control (much like drag on a fluid pan/tilt head), adjustable arc diameter crank handle and guarded side rails for the most versatility, this flagship product will handle anything you put on it.