We just released when.js 2.3.0. This release has a new promise.tap() API, faster promise resolutions, faster "time-to-first-handler" in environments that support MessageChannel, and internal architectural changes that pave the way for when.js 3.0.0!
The 2.3.x line is likely to be the last in the 2.x releases. We're already hard at work on 3.0, and it's going to be awesome: highly configurable/extensible core, extendable promise subtypes, and more ...