What are the node.js frameworks for real-time model synchronization between browser and server?

You can look into:

• node-object-sync https://github.com/jonashuckestein/node-object-sync ,
• backbone.iobind https://github.com/logicalparadox/backbone.iobind or
• backbone.io https://github.com/scttnlsn/backbone.io

but racer / derby is not bad either. These are just options, you should pick one whichever is most appropriate for you.

I suggest you continue using Racer, or, if you are interested in a more mature framework based on Racer, I strongly suggest you try out Derby.

If you are coming from Rails, I would totally suggest you go all in with Derby. If you are looking for a Rails Backbone alternative for Node, try Backbone.io

Adding for completeness: Meteor DDP: https://github.com/meteor/meteor/blob/master/packages/livedata/DDP.md

The best way to use it is to go all-in on Meteor; I doubt that the code is useful or usable outside of Meteor. The spec may be, though.

For real-time application development, currently, we have Derby and Tower.js