What are these lights called?

Hiya,
im looking for a low voltage lighting system for a kitchen. I've seen a setup before which essentially has the lines (a bit like an overhead tramline) on the ceiling allowing you to attach the lamps wherever you want. Problem is I don't know what an earth they are called so can't start looking for them! Anyone know what they are called and where I can find them? Cheers!

 

That's exactly what I am looking for. Nice one Snezza!