I would like to introduce a project I've been starting today. It's called N-Ext (compression of Node and Ext), and its purpose is to bring the power of ExtJs to the server through Node.js.
Its set of features is currently very limited, but it includes the dynamic class loader package and the Ext.data package.
Those two were for me the most important to include because the data package allows to check the consistency of the model on the server without having to implement the model twice (once on the client for Ext, once on the server), and Ext.data makes a heavy use of Ext.require.
In a very near future, some proxys will allow to store data in a variety of DBMS. More features are to come, but the plans to listen to the potential users' requests to define priorities for the project.