If you're interested in the nitty-gritty, technical changes to the Spawning Tool, you can find the commit logs for spawningtool on GitHub

If you just want the big picture on feature development, check out the Spawning Tool posts on Kevin's blog

And if you want something in-between, the change log is below.

The Actual Change Log

June 2015May 2015April 2015March 2015December 2014November 2014September 2014August 2014May 2014April 2014March 2014November 2013September 2013August 2013July 2013June 2013May 2013