TurnAbout is a free Internet multiplayer Arcadia game creator which allows you to craft and share your own multiplayer games, using the Arcadia multiplayer game/chat/server environment. It comes with some games to start you off, then you add more! TurnAbout comes with Blackjack, Feud, and WindChasers (a sailbot racing simulator). Your new games are written in Lua using the TurnAbout API (http://www.synthetic-reality.com/turnAboutAPI.htm). The TurnAbout API lets you focus on your game and take advantage of Arcadia for graphics, sound, and networking/server support.
Lua is an easy to learn language with instant gratification (no compilers needed, you just need a text editor -- I suggest TextPad with the lua syntax highlighting module, but notepad will do.)
This is perfect for the budding programmer looking for an easy environment to develop multiplayer game ideas, or for the professional who is just looking for a place they can whip out a functional game in a few hours.
TurnAbout also includes a heirarchical card editor (cards inheriting properties from other cards) which can be used to easily create cards-based board-games (think: Monopoly), if you like, or you are free to just take over the screen and do whatever you like.
The TurnAbout API is in constant development, so be sure to ask for anything else you need.
This game is part of the Synthetic Reality "Arcadia" family of games. (http://www.synthetic-reality.com/arcadia.htm) Players add additional channels at will using the integrated MIX server. Arcadia itself provides all networking support, in addition to text chat, voice chat, web browsing, and a parallel existence park environment for serenity, duck-feeding, and paintball while you wait for other players to show up. Arcadia allows you to create a personal identity with which to expose your current emotional state, and maintain a diary of other players you have met in the game.