More and more people are using io.js now, and they have more releases, using a stable engine, already reached v2, I'm sure others will add more to this list.
Some important people from Node forked it into io.js. They want to release quicker and stay on the cutting edge. IO.js is managed by consensus, whereas Node is governed by Joyent. Some were upset at the slow pace of node's progress, accusing Joyent of holding it back for "compatibility" reasons.