Ruby Swords are useful items in Minecraft. They are somewhat hard to obtain because of the need for rubies when crafting them. They are stronger than iron swords but weaker than diamond ones, and they do not break easily. You can only got this with mods.
Ruby swords have a durability of 752 hits and deal half a heart more damage then an iron sword. They will kill some mobs in one hit (chickens and others) and, because of their high durability, can be used many times and are considered a "cheaper version" of a diamond sword.