Entanglar is an upcoming networking framework for the CLR. It is aimed at the casual game developer - providing automatic and transparent networking, the "spooky action at a distance", that lets you bring multiplayer to your games simply by adding [Synchronised] attributes on your properties.
As a downside, it is in an early alpha stage of development. Upside is that it comes with a wrapper for the Box2DX physics engine, which is used to demonstrate the remote error prediction and sync.
I'm very interested in people's opinions on how this works with the existing XNA pipeline / their needs. At I haven't specifically targeted XNA, Entanglar currently comes with its own timer code. Later I plan to add a wrapper for the existing XNA game loop, and work on compatibility with the CLR on the 360 (doubt the use of DynamicProxy will make it happy at the moment).
Entanglar doesn't come with any graphics, sound or input - I assume people have their own preferred options here anyway.
If anyone is interested in taking a look, it can be downloaded from http://entanglar.dunnchurchill.com
Cheers,
Mark