Unity 2 Multiuser Development Kit (Unity 2 MDK) is a complete framework for creating and deploying multiuser applications in Macromedia Flash. Unity 2 MDK includes:

Unity 2 Multiuser Server
A server-side development framework and multiuser socket server. (The Unity 2 Multiuser Server is also available separately for use with Unity 2 App Packs and non-Flash clients.)

UClient for Macromedia Flash
A client-side development framework that lets Flash developers create multiuser applications entirely with ActionScript, without writing a single line of server-side Java code.

• Easily build sophisticated multiuser applications entirely in Flash, without server-side or Java knowledge.
• Create any kind of multiuser application (not just games or chat) with a completely generic multiuser toolkit.
• Deploy ready-to-use Flash apps, including: SimpleChat, MultiRoom Chat, and Tic Tac Toe.
• Customize existing samples or develop from scratch.
• Permanently store data in a database or to the file system (MySQL support included or write your own data storage implementation).
• Manage up to 2000 concurrent user connections (depending on application demands, CPU speed, memory, network load, and machine thread limits).
• Group users in different rooms.
• Automatically share data between users, or execute code on other users.
• Kick and ban users via an administration tool.
• Auto-kick idle users (configurable).
• View connected users and rooms in a web-based server admin tool.
• Run multiple applications simultaneously on the same server.
• Debug with extensive, configurable client and server logging.
• Develop clients in Flash, Java, C++, or any other socket-based platform.