It's been a while since I linked to any games, so here for your amusement and delight (via Mefi) is Castle Wars. It's pretty easy to figure out, but here are the basics:

* Each turn you must play one card, or else discard by hitting CRTL + click. The number in the upper-right corner is the cost in crystals (blue), weapons (green), or bricks (red). The effect of each card is clear from the card's bottom.
* Each builder, soldier, or sorcerer makes one brick, weapon, or crystal a turn.
* Win by either destroying your opponent's castle or building your castle past 100.

There's a netplay option too. Happy Saturday.