At its heart, every single MMO is a game about collecting things. Most games have a number of very obvious things to collect; collect the best gear in World of Warcraft, collect money in ArcheAge, collect AP in The Secret World. There are usually optional extra things to collect, as well, like different equipment looks in Guild Wars 2 or extra max-level classes in Final Fantasy XI. With a broad enough definition of “collecting,” you really can look at every single MMO as the art of collecting more of something, as long as “something” includes “experience” or “skill points” or the like.
But there’s nothing forcing you to just work with what the game tells you to collect. You could collect mounts in Final Fantasy XIV. You could collect pets in WildStar. You could collect account-wide unlocks in Star Wars: The Old Republic. You could even go completely off the wall and collect weapons, or collect friend list entries, or collect vendor trash that you find amusing. (I actually usually collect a few pieces of otherwise useless memorabilia in any given game, myself.) What about you? What do you collect in MMOs? What’s the weirdest thing you’ve ever tried to collect?