Cro-Moly is a type of steel and is generally considered a "safe bet" in the sense that it's durable, has good strength, is reasonably lightweight (as far as steel tubing goes) and can be manipulated and welded easily. There were many different brands of tubesets made from Cro-Moly steel. I had a Nishiki Ariel MTB made from Tange Prestige (a form of 4130 Cro-Moly) that rode wonderfully, was comfortable on long rides and survived plenty of offroad trail abuse. However, bear in mind that we're talking steel here and thus you need to perform careful inspection for rust.