Every once in a while this site passes within my field of view. This time it is because someone on BGG noticed a game submitted to the site that plays with a standard deck of cards and duplicates most of the gameplay of Havoc (by Sunriver Games). K.C. of SG, the designer of Havoc, was cool about it, although he did request some sort of acknowledgment be placed on the page. Morally, he's absolutely right; legally, I doubt he can enforce it unless he has trademarked the name "Havoc" or "The Hundred Years War" for card games.
Pagat is not an attractive site, but it sure contains a heck of a lot of games and game information. The games are all card and tile games. They are organized in various ways, such as category, country, and alphabetically. Complete rules and variations are described. Most fascinating are the hundreds of original games contributed by the readers, which are also described.
Each time I see the site I promise myself that I will go through it. I think that I shall. I'll let you know what I find. If anyone already has some favorites from this site, do tell.