I just found out about a new mod for Terraria releasing soon called Super Terraria World. STW is a standalone MMORPG style Client and Server for Terraria that adds an RPG feel to the game by adding quests, leveling, and a ton of new weapons, armor, NPCS, and more.
STW is currently in a single player open Alpha, so you can mess around with it if you’re brave. Installation instructions can be found here/
If STW is something you’re interested in, you can keep track of the latest announcements here.