Initially the project was just an experiment with no real intent to open source it. So my 30-seconds name for the repo become Mobservable (contraction of mob and observable; a lot of observables). When I OSS-ed it, i figured that Mobservable wasn't really about an api for observing data, but about reacting to data. So I started looking for a new name and ended up with MobX: short, still relates to Mobservable, and the X hints to reactivity. The "Mob" can also refer to the mafia, which nicely conflicts with state management :-), and might be fun for a logo (which I never got to, so suggestions are welcome ;-)).