React-redux v5.0.0
github.comNot sure why this is on the front-page. This is just a glue library between two other libraries and the update doesn't seem to be a real major update.
"Version 5.0 maintains API compatibility with v4.x but due to major internal changes and potential behavior differences across nearly all API surfaces, semver dictates a major version bump. Also, it's good marketing!"
Anyway, the marketing part worked. :)
React and Redux are both popular and widely used, and this is the official library that ties the two together. Also, it's absolutely a major update. The API is almost identical (with one new function), but the internals were completely rewritten, with potentially different (but better) behavior in a few edge cases. It also offers improved performance in most cases.
See https://github.com/reactjs/react-redux/pull/416 for the nitty-gritty details of what was involved.
Gotta keep the hype train rolling. All aboard!