One-Shot Executor is an infrastructure plugin, it does not provide new Slaves by itself, but just the API for a Slave provider to implement this new approach and only focus on running a Slave according to the Job configuration / Build parameters.
Implementation currently uses terrible hacks, but is working well. We use it as a proof of concept and a way to demonstrate need for new hooks in jenkins-core, so a future release could use cleaner APIs and not rely on some Jenkins internal implementation detailsrequire Jenkins 2.9 or later as we had to introduce some dedicated hooks to allow the Build:Executor inverse relation.
This plugin has been extracted from dockerfrom docker-slaves, we created for Docker Hack Day 2015 (we won the 3rd prize!), and which is an experiment sandbox for us. So this specific piece of code was created by extracting stable components to let them become mature and usable by others.