The Magtube is a RedPower item. It is an enhanced item transportation tube which is used to speed the traveling of items in tubes. It is generally used for transporting items long distances. To begin using Everything in RedPower, you must have Accelerators: One for the end you are speeding up, and one to decelerate the object when it is to come out of the Magtube. Then, provided the accelerators are powered with Blutricity, you can begin moving items down the Magtube.
Items in the tube are transported at a speed of 1 block per tick (i.e. ~20 blocks/sec), which is 15 times faster than through a Pneumatic Tube. Note that, similar to Buildcraft's Gold Pipes, this does not increase the overall efficiency in any way, it only makes blocks move to and from faster. This could be handy for trade systems on servers, for example, as the long waits incurred by slow moving Pneumatic Tubes could not get annoying to players.