Thanos Rummy Games
Thanos Tsakonas runs a site called Thanos Cardgames, where he distributes a huge number of free card games he's written, including Rummy games such as Rummy, Carioca, Kaluki, Koum Kan, Loba, Panguingue, Thanassis, and Three Thirteen.
In addition to the Rummy-style games, Thanos also offers "climbing games" such as "Big Two", "fishing games" such as "Ronda" and "Zwickern", "matching games" such as "Mau-Mau", and "trick-taking games" such as "Alouette", "Briscola", Preference", "Rentz", and "Smear". There are nearly a hundred games in all.
What you'll probably notice is that Thanos likes to focus on the less well-known regional games and variants, as opposed to the common every-day card games most people are familiar with. In many cases, his games are the only implementations of the games available anywhere.
All the games are freeware, and although there's not a lot of flashy graphics or animation, the visuals are very nice indeed, with large and details playing cards.
The one area where the games are lacking is in help. There are no in-game menus, rules, or help screens. And the games are played full-screen, so it's not easy to keep online rules open as you play. The interface is mouse and keyboard driven, and while it works fine once you get used to it, it's confusing at best when you're just getting started.
Still, this is a great collection of games, and well worth checking out if you're looking for unusual games.