This week's free store item is a Universal Solvent, use the code UNISOL before 5/17. It is used to craft essences. If you don't have a level-cap character that can use it, you may still want to get it. They have recently been selling for 30-40g.
It is delivered in a box that is bound to account and you must be at least level 50 to open it. Once removed from the box, the universal solvent is unbound, so it can be traded or sold on AH. They can be stacked to save space if you prefer to save it for later. If you do not have a level 50+ character, the box can be mailed for 2 Mithril Coins.