Microsoft Edge started as a IE fork but later departed considerably from it in an attempt to break with the past and legacy Internet technologies, removing 200K LoC but adding other 300K. Microsoft says they want “better interoperability with other modern browsers, improved performance, security & reliability, and reduced code complexity.”
Facebook has released React v0.13, bringing with it support for ES6 classes, as well as new top-level APIs and breaking changes for JSX.
Node.js has released version 0.12, its first significant release since 2013's 0.10. The much-anticipated version 0.12, once described as "imminent" in January 2014, comes with a raft of Module and JS API changes, an updated version of V8, and many debugging enhancements. Significantly, it also comes with initial support for ECMAScript Internationalization API 1.0 (ECMA-402).
CoffeeScript 1.9 has finally introduced support for long awaited generators, which promise to prevent callback hell and help writing async code.
The io.js team has released version 1.0 -- but the versioning does not suggest the platform is "production ready." Despite overtaking Node, io.js clarifies the release in its own FAQ: "The choice to release as 1.0.x was not to signify that io.js should be considered production-ready, but because it was a significant enough release from Node.js to warrant a major version increment," it says.
Ecma International has standardized the first edition of Dart, ECMA-408.
The NodeJS based Koa web application framework has released version 0.2.0. Koa is the successor of the popular Express MVC platform, but relies heavily on newer ES6 constructs. This release is marked as an important one in that that it reaffirms the team’s design choices from the initial 0.1.0 release, solidifying Koa's API for future releases and production use.
The recently released Dart 1.1 comes with better performance for the dart2js compiler and improves support for the server-side development. The language itself is pretty much on hold.