Alchemy Cape
Alchemy Cape is the mastery cape of Alchemy: only those who took that profession to level 100 wear it.
How to get it
Take Alchemy to level 100 and talk to Teo, alchemy apprentice: they give you the quest Mastery: Alchemy, and turning it in grants the cape. It is the only way to get it.
Who can use it
Any class can equip it.