Rack is probably the most important project for the Ruby world since Rails. Allowing any ruby web framework to work seamlessly with each other should help propel the newly competing web framework as first class citizens, to be used easily alongside Rails .<p>Soon we'll see Routing, Authentication, and Debugging all using Rack middleware instead of framework specific plugins.
Congrats to the core team and all of the contributors!<p>For those who haven't checked it out, the spec is surprisingly short (<a href="http://rack.rubyforge.org/doc/files/SPEC.html" rel="nofollow">http://rack.rubyforge.org/doc/files/SPEC.html</a>).