It's a spectacular release. I've been waiting for some of the features for a long time (\K, recursion), but Jan went even further. For instance you can convert between different languages.
Free demo: http://yu8.us/rbdemo
Glowing review:
http://www.rexegg.com/regex-tools.html
Release notes: http://yu8.us/rb4release
It's big news in the world of regex so will be cross-posting my two other favorite regex boards.
W00t!