Lets you use "tools" in unusual ways, such as from shell scripts.
See http://issues.jenkins-ci.org/browse/JENKINS-4532 for motivation.
Some screenshots are better than a long discussion:
Compared to Custom Tools Plugin the advantage is that you can use the tool in arbitrary ways, not just running an executable from it. In the future these plugins should be merged. SharedObjects Plugin can also be used to achieve this plugin's effect.
1.0 released Feb 15 2010