There’s a legal case brewing that might have implications for the RPG world. For a long time, RPG companies have held people who wanted to make compatible products at bay with legal threats; even though the rough consensus is “you can’t protect game rules” there hasn’t been clear enough case law to make it “safe enough” for people to bother.
However, now there’s a big test case – with Hasbro involved no less – where they’re suing an online game called Scrabulous that uses the same rules as Scrabble.
If Hasbro etc. loses, this means that there’s a lot clearer protection for other people – for example, for people or companies to make D&D compatible products without having to deal with Hasbro/WotC’s ideas of how that should happen. Check out the linked article for some legal analysis from an IP attorney.