Finally, there's a way to repair enchanted items and another use for XP! I present to you, the anvil!

What exactly are they?

They're anvils, and can be used for a variety of things. You can make them with this crafting recipe:

What's their uses?

Renaming Blocks & Items

One of the new features anvils brought with them is the ability to rename any block or item. To do so, simply right click on the anvil, put something in the item slot, then type a name into the large box.

Repairing Enchanted Items & Combining Enchantments

For the cost of quite a lot of XP you can also repair enchanted items. This is done by putting two of the same sortof broken tools into the slots available. The enchantments on each tool will combine into one, so you could put an Eff I pickaxe in one slot, and an Unb I in the other, and you'd get an Eff I Unb I pickaxe in return.

Sometimes the enchantment cost is so high, it makes more sense to just craft a new version of whatever you were going to repair, and enchant it from scratch. The best time to use anvils is when you get a rare and amazing enchantment you want to keep at all costs, since you'll be guaranteed to keep it in a repair.

Misc. Uses

While not intended for the purpose, you could use an anvil as a trap to protect your house on servers that allow it, as they cause damage to anything they fall on. Also, they'd fit right in if used right in a medieval adventure map.

Do they last forever?

Nope. They last about 25 uses if just used for renaming and repairing - although this will be lowered if you enjoy pushing your anvil off cliffs, causing them to take fall damage. You know if an anvil's near to breaking, since when it is, it turns into a "Very Damaged Anvil".