Redstone Tubes are the same as Pneumatic Tubes except they carry a redstone signal. The idea being that using a Redstone tube can carry both items away from a machine, and a Redstone signal to that machine, without having to run separate Redstone and Pneumatic lines (note however that the standard signal distance of redstone dust is used, not the unlimited signal distance of wires).
For example, a series of Filters connected to Singularity Compressors could be used to pull finished product out of the Compressor when they receive a signal. The Redstone Tubes conduct the pulse to the Filters, while simultaneously carrying the product away from the Filters.
Redstone Tubes can be connected to standard Pneumatic Tubes, allowing a player to 'separate' certain machines from the Redstone signal the Tubes conduct.
Note: Shapeless recipe.