I've been using Fluxxor http://fluxxor.com/ for a relatively large application. Has been working well! When I started the project the flux concept was still very, very new and there were not many implementations. It took care of the basics and has gotten out of my way. I'm looking forward to trying marty out on a new app.
which looks a bit like reflux in terms of terseness but it adds the ability to have snapshots and rollbacks, isomorphism, and it plays real well with ES6.
I'm using Reflux for now, though I'm tempted to switch to something more FRP like Bacon, f, or RxJS. I find that I end up making stores for both AllThings and CurrentThing, and it should be easier to express that relationship with FRP.
I really like Reflux as well. In a recent project I used Bacon.js[1] to create my own implementation that ended up looking similar to Reflux.
The project involved asynchronous requests triggered by the actions, and transforming & aggregating the returned data. Compared to Reflux, Bacon made it very easy to do this by composing small functions that are applied sequentially to a stream of actions.