I have been playing with the idea of grabbing art work from open source software and wish to start a forum discussion on the topic as a informative.
First, please be aware that not all "open source" software is free to use anyway you want. If you intend on placing something you make that is derivative from the original software in circulation you must abide by the specific license of that software. Some licenses prohibit commercial sale or modification of the original game/content, while others allow commercialization but you are unable to copyright the derivative work as your own. If in doubt don't, or consult a lawyer. I'm not one.
That being said, check this out:
There are many games to choose from with different types of licenses. Some are more strict than others, so read their licence descriptions carefully. After that its just a matter of finding said software.
Some of them can be found here: