XadrA Fortress: www.xadra.com
Background
Brought to you by the team that built large-scale game servers for Sony Online, Disney, Shockwave.com, and others. They’ve condensed what they learned into Fortress.
Features
[*] supports 1000’s of simultaneous users
[*] comes with a license that permits 50 simultaneous users, so smaller sites can run for a long time before shelling out any money
[*] the important parts of the server can be extended/overridden, and there’s plenty of documentation (including Javadoc) so you can extend Fortress to your heart’s content
[*] built-in “message reflector” subsystem, making it easy to build “party-line” applications
[*] built-in “room” subsystem, where each room can have a plugin to hold custom game logic and state
[*] built-in “instant messaging” subsystem, where each user has a friend list (online/offline status notifications) and an enemy-list (message-blocking)
[*] built-in “game-matching” subsystem to automatically match similar users into game rooms
[*] open-source client-side frameworks for J2SE and Flash (J2ME also available, but not for free yet)
[*] plenty of working samples, both client apps and room plugins
[*] all communication between client and server is in XML
[*] hot connection permits client and server to act as peers, sending messages at any time (a.k.a., server push)
[*] runs standalone or inside bigger Java app servers
[*] JMX-based server framework with web-based management console
[*] server can be accessed by any XML-capable client platform - J2SE, J2ME, Flash, C#, etc. - and the server-side game logic doesn’t know the difference
Requirements
[*] Java 1.3 minimum
[*] Java 1.4 preferred