SEE VULNHUB ~ http://vulnhub.com
Pentest lab. "Hacker" training. Deliberately insecure applications challenge thingys.
Call it what you will, but what happens when you want to try out your new set of skills? Do you want to be compare results from a tool when it's used in different environments? What if you want to explore a system (that is legal to do so!) that you have no knowledge about (because you didn't set it up!)...
If any of that sounds helpful, below is a small collection of different environments, so if you want to go from "boot to root", "capture the flag" or just to dig around as much as you want to try out the odd thing here and there. These will allow you to do so and without getting in trouble for doing it!