Are there any docs on Rack 2.0? Like, what's changed to warrant the bump in the major version?
And is the project page still at http://rack.github.io/? The latest item in the _news_ section is from February 2013 about the release of 1.5.2.
It's really obscure, but I found these in the root directory:
https://github.com/rack/rack/blob/master/NEWS
https://github.com/rack/rack/blob/master/HISTORY.md
That covers through end of 2015 as of today, but nothing really specific.
The pull request milestones don't look to be completed, but there is a non-pre-release for 2.0.0:
https://github.com/rack/rack/milestone/11
https://github.com/rack/rack/releases
Best we've got for now may be to compare the versions with a diff and examine the commits.
Changes are now described in CHANGELOG, which has been updated to describe what is new in Rack 2.0 and later.