Adobe Flash Builder4 beta 2 is available on http://labs.adobe.com for downloading. One of the themes of Flash Builder 4 is to make data-centric development a lot more easier. You can find articles on developing Flex application for various server technologies using Flash Builder 4 at this URL http://sujitreddyg.wordpress.com/flash-builder-4
The Data Centric work flows in Flash Builder 4 are designed to be extensible i.e. you can add a new plugin to Flash Builder by implementing the interfaces exposed by Flash Builder and add support for any back end of your choice.
Gaurav Priyadarshi from Adobe Flex team extended to add support for consuming AMF(Remoting) based services running on a Ruby on Rails driven server.
You need Flash Builder 4 beta 2 to use this plugin, download and install Flash Builder 4 from this URL http://labs.adobe.com/technologies/flashbuilder4/ and then follow instructions below to set up Ruby on Rails plugin.
Please download the plugin and install from this URL http://dcdror.riaforge.org/
Details on installing the plugin and setting up Ruby on Rails project can be found at this URL http://dcdror.riaforge.org/blog/index.cfm/2009/10/9/Using-Ruby-On-Rails-plugin-for-DCD
Details on using the plugin can be found at this URL http://dcdror.riaforge.org/blog/index.cfm/2009/10/9/Using-the-plugin-from-FlashBuilder4