I worked at a restaurant for a month once and they had a device there. It was a rectangular box: you'd put a tomato in it, and there was a handle at the one end you could use to push the tomato against some blades. The tomato would come out the other end in 5 slices.
It was so much more efficient than using a knife, but I don't know what it was called.
I almost want to say it was a tomato slicer, but I never heard anyone call it that.