Bukkit

I'm going to try my best to describe this

A command, to open up an item menu. In this menu, it would list all of the achievements, and if the achievement has not even completed yet, it will show coal, and if the achievement has been completed, it will show a Diamond.

You could list the name of the achievement as the item name, and a short description of the achievement as the lore.

So, coal would be in the place of an achievement that has not been unlocked, and a Diamond if the achievement has been completed.

This server did this concept, but an unlit torch represented an achievement not unlocked yet, and a lot torch represents a completed achievement.
A screenshot: http://imgur.com/rIj80wP