While I was reading Machine Design today, I noticed a supplier that has some products that could be useful theatrically speaking.
Its the Pacific Bearing Company at http://www.pacific-bearing.com/about/.
What caught my eye was the redi-rail. Its a track in which the slides are wheels /rollers that run horizontally in the track instead of vertically like most common track. Testing / more information would be needed before using this overhead, but for tracking scenery at deck level, I see this as not only an interesting product, but a product in which adaptations could easily be made to use in house.
They have a range of other products as well, including some meant to be motor driven.
Check it out.