This ruling is sure to be of interest to all tabletop games makers.
DaVinci had sued Ziko games over the game Legend of the Three Kingdoms, which both companies acknowledge is mechanically identical to DaVinici's board game Bang! The art and aesthetics of the two games differ, with Bang! taking on the iconography of the wild west and Legend of the Three Kingdoms borrowing from Chinese history.
The court's ruling, which Strebeck has hosted on his own site, states that nothing about the mechanics of Bang! can not be considered "expressive," as they are rooted in widely familiar game concepts like health bars, punches, and kicks, while that the expressive elements of the game (its art and aesthetics) aren't substantially similar to Legend of the Three Kingdoms.There have been examples in tabletop games such as Monopoly clones, and of course CCG's that are all essentially clones, or close facsimiles, of Magic: the Gathering*. In the case of Monopoly Hasbro has been vigorous in defending the expressive aspects of Monopoly such as the look, trade dress, and characters, but not so successful in preventing mechanical clones. For example: Triopoly, Petsberry, and Cashpiracy. Granted, these games do add some mechanical variations and improvements, but the similarities are stronger than you'd think they could get away with.
With all the wrangling around what is protected under "OGL", what is "d20", what is this or that, I wander how much legal protection any game system actually has. The expression of the game, it's "world" and art, such as Dungeons & Dragon's Forgotten Realms, or Runequest's Glorantha, or Traveller's Charted Space, seems to be what is protected by international copyright laws.
The full article is here: http://www.gamasutra.com/view/news/273935/Texas_court_affirms_game_mechanics_not_protected_under_copyright_law.php
Of additional interest, read the fascinating case of the battle for Anti-Monopoly.
Also related; according to the US Copyright Office in their publication on Games, fl-108, “Copyright does not protect the idea for a game” . . . “Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles.”
Here is a more detailed analysis by Zachary C. Strebeck, attorney at law (tip o' the hat to Sean Kelley)
*note that in the case of M:tG Wizards of the Coast got a patent on the core game mechanic. I don't know if they've exercised that in a legal case.
None of this is suggested to be legal advice of any sort, as I have no qualifications to give such advice, I'm merely passing along this info from other public sources.