Google Chrome has been catching up pretty fast in the war of browsers. Since its first release in Q4 of 2008, it has released 4 Major versions of the browser and is all set for Release version 5, with beta being released. Firefox a competitor from over 5 years is still has its most stable version as 3.6, which clearly depicts how fast Google is running. But they are not very sure what is a major release, instead of having subversion of Chrome they release it as next Version.
For information about alpha and developer builds, check out the Chrome dev channel here.