We're happy to finally introduce (experimental) WebSocket support today. You can now select the "Beta" region when creating an application to try our latest environment, and we hope you'll help us test it with your own .NET and node.js apps.
The "Beta" region runs Windows Server 2012 application instances in the US (AWS US-EAST) with IIS8, node.js (0.8.20) and iisnode (0.2.3) and is otherwise identical to the current environment. Along with nginx this allows you to leverage WebSockets for your .NET and node.js apps.
We're still ironing out some kinks before we're ready to fully migrate to WS2012 and IIS8 and the WebSocket-enabled version of nginx was just released - so it will be a little while before we feel confident about migrating all apps. With the new region you can try how your applications actually work before we make the move to the updated environment. It will be updated frequently and is generally less available than our regular US and EU regions, so make sure not to use it for your production apps.
Here are a couple of sample apps using WebSockets on AppHarbor:
That's it! Take it for a spin and we look forward to your feedback.