Sony Online Entertainment has revealed Player Studio, a program that allows players to build in-game items of their own for a select (and expanding) library of titles. As the official website explains it, you'll "download sample geometry, learn how virtual items are constructed, and try designing items." This also includes naming the thing and writing a description that suits the target game's narrative.
Player Studio only includes support for EverQuest and EverQuest 2 at launch, though the website indicates that added support is coming soon, for FreeRealms and Vanguard: Saga of Heroes. The site also notes that, while the program isn't fully up and running right now, you can read about how it fits into each game and get started on your item building. Simply follow the links on the homepage to the relevant game's Player Studio portal.