Could be he meant free as in "free speech," not free as in "free beer." Though I suspect he wants both...
If I may make a suggestion, as someone noted, a "simple" system is not that great for a computer game... However a complicated system, on the other hand, is absolutely perfect for a computer game. It doesn't matter how inconsistent or hard to memorize/learn the rules are, the important thing is that the rules are thorough in coverage and adjudication.