I've been spending a little bit of time with node.js in the last few days and although I have not yet built anything meaningful with it I'm already quite impressed by it - despite it being JavaScript based :-)
In case you don't know what node.js is, let me give you a short intro (if you are familiar with FMS's AS1-based server side syntax then you'll quickly feel at home with node). Combine this with node's event based nature (everything in node runs asynchronously with extensive use of callbacks) and you can see how there is also some similarity with the events you may be used to from ActionScript3.
The fact that node is both asynchronous and single threaded means that every operation it runs is non-blocking, making the platform extremely scalable when it comes to handling large numbers of concurrent requests. LinkedIn for example have apparently had great results porting some of their apps from a Rails backend to node. Reportedly they went 'from running 15 servers with 15 instances (virtual servers) on each physical machine, to just four instances that can handle double the traffic'.

For me at least that sounded interesting, although I have to admit that I do not have any scaling or capacity issues using any other (thread based) server technology so far. Instead what attracts me to node is the similarities both in lamguage and syntax as well as in functionality (node is great for building real-time apps with add-ons such as socket.io).

The most-used example of a simple node.js app is probably this http server from the node.js homepage:

view plain
1var http = require('http');
2http.createServer(function (req, res) {
3 res.writeHead(200, {'Content-Type': 'text/plain'});
4 res.end('Hello World\n');
5}).listen(1337, "127.0.0.1");
6console.log('Server running at http://127.0.0.1:1337/');
It almost requires no explanation at all. Once started it will respond with 'Hello World' to every request. But as I said I have not actually got any code of my own to share right now, but wanted to point you to a great resource for getting started with node which is this page from smashingmag. It has a ton of links to other sites, all containing tips and tricks around node. I found nodebeginner.org particularly useful, but please judge for yourself.

Do you use node? Maybe in combination with a Flash based frontend (I think this would make for a great duo...)? Please leave a comment if you do (but don't hesitate to comment if you don't), and include some demo links if you can.