Yesterday the first stable version of io.js was released. io.js is a major fork of Node.js by its core developers. The reasons and the process of forking are best summarized in the Isaac Z. Schlueter's (a former Node.js project lead) blog post.
The release signifies the end of the stagnated technical progress of Node.js. However, the most important change is not technical. Unlike Node.js, which is guided solely by a single company decisions, io.js uses an open governance model. This opens up the development for more contributors. There is also a strong intent to bring more regular releases. Under Joyent, even long announced releases did not happen.
Despite all the changes, io.js intends to stay compatible with NPM and the packages it contains. My own experience with compatibility has been very positive. My largest Node.js project (an Express web app, ~20kloc) worked without any modifications when running on io.js. Also, some of the routes saw 2x req/s performance increase. However, if your project contains native packages, you might expect some issues compiling them due to changes in the V8 API.
Congratulations to the io.js team and contributors for the release!