I've always wanted to create a web based game, similar to the other web based games such as
Kings of Chaos,
Legend of the Green Dragon etc. I even planned to write something in ASP.NET 2.0 and I still might (given time). Probably not however, since I am enjoying so much of DotNetNuke work and
have plenty to do as well!
Back to the topic though, open gaming, similar to open source is the sharing of rules between games. It's typically the rules that are the hardest parts of the game to come up with, so targetting a genre is relatively easy.
The advantages of using a common rule base, is that the players of your game are familiar with the general rules. Something like
Wizard's D20 rules which has an open game license is an example of this. It's a really simple game mechanic but very effective. I've been tempted to incorporate this mechanic into a game.
Although you need to be suspicous of some companies motivations to distribute an Open Game license. Unlike DotNetNuke's open source license, Wizards of the Coast are free to modify the license at any time, making it a risky gamble to produce a product based on those rules. (This is merely what I have read, and I do not have a complete understanding of their license)
I wonder what other types of IP will become Open Source in the future?