PureMVC is quite a versatile MVC kit.  With implementations for AS3, .NET (c#), Python, PHP, Silverlight and other platforms it is quite a system and domain to spread that far and have consistency.  There are small changes but for the most post the MVC is the same structure across the platforms.  This can be very beneficial for a service firm or for a product base that needs to support many different platforms.

PureMVC is a lightweight framework  for creating applications based
upon the classic Model-View-Controller design meta-pattern.
This free, open-source framework is implemented in ActionScript 2 and
3, Java, C# and a number of other popular programming languages.
This allows development on a wide variety of platforms including:

• Mobile Environments: FlashLite, .NET Compact Framework, J2ME
• Server Environments: ColdFusion, J2EE, PHP, Python
• Browser Environments: Flash/Flex, JavaFX, Silverlight
• Desktop Environments: .NET, AIR, FLASH, J2SE

For Flex PureMVC happens to be my favorite MVC kit.  I only use one if absolutely necessary but PureMVC keeps it clean.  The great thing is that is works with or without Flex unlike Cairngorm and it is always up to date.  It is just an added bonus that is spans so many other platforms. There are a few things I don’t like about it in other platforms like the url naming but it is much better than kits out there now and Microsoft’s ASP.NET MVC most likely wont’ be cross platform *wink*.

Some info on the PureMVC framework (caution PDF):

• Goals & Benefits
• Conceptual Diagram
• Framework Overview
• Best Practices

PureMVC Manifold

• Documentation
• Project Owners
• Repositories
• Get Involved!

Ports

• ActionScript 2
• ActionScript 3
• C#
• ColdFusion
• Java
• Perl
• PHP
• Python
• Ruby
• Propose a Port