I believe it is Euphorbia tirucalli, often incorrectly called Pencil Cactus. It is not a cactus. If cut will bleed white latex which can be a skin and eye irritant. I have one myself, of the 'Fire Sticks' variety.

Christopher

It looks like a euphorbia tirucalli like stated earlier. Seems to be a few years old, as the limbs have fused and make a sort of trunk. Be careful with it as it has irritating latex sap inside. I have an E. tirucalli myself, but it's not very old and is only about half a foot tall, but it is growing rapidly. Got it a few months ago and it was only about 8 cm tall. It puts out new limbs fast