Keldon Jones has published an artificial intelligence opponent for the game Blue Moon with an user interface written with GTK+ toolkit. This is a native Mac OS 10.5 version of the game written with Cocoa, so there's no need to install X11 and GTK+ libraries. It runs straight out of the box (on Leopard).
Here is a compiled application package ready for use. Just extract and move 'Blue Moon.app' to your Applications folder.
The following package contains the source code and other necessary additional files to compile the game with Xcode 3.0 on Leopard. You will also need the Blue Moon AI 1.1.2 source package from Keldon's Blue Moon AI page.
So, first you should download and extract Keldon's Blue Moon AI source. After that you can extract the Mac OS source package into the 'bluemoon-1.1.2' folder. To compile, open Terminal and go to 'bluemoon-1.1.2/mac' folder and type 'xcodebuild'. Of course, you can also build 'bluemoon-1.1.2/mac/BlueMoon.xcodeproj' project in Xcode 3.0.
These screenshots show you what the game looks like. It is really very much like the original user interface. You can choose decks for yourself and the AI by clicking on the leader cards at the right side. Next to the leaders you can see discard pile, deck, combat pile and support pile (from right to left). Leftmost there is a magnification of the card the mouse is over, so you can see details of the card. Cards in your hand are in the bottom, cards in AI's hand are at the top.
You can start the game by clicking either of the 'start' buttons below the large card preview. After that you play, retrieve and satisfy cards by clicking them, just as in the original. To play a card without an optional effect, you should click it with alt key pressed (in the original UI you would middle-click).