I took a look at node.js for my latest project because it could seriously benefit from the asynchronous nature. I found that the ecosystem was too fractured for me to be able to quickly determine what would work best. What's the best node stack for someone coming from the rails world to use?
I recommend Express.js ( http://www.expressjs.com ). It's Sinatra-like and gives you static pages, sessions, and HAML/SASS templating. I've been using it with the project node-mongodb-native leveraging MongoDB as a datastore (although the Mongoose project looks like it might be a cleaner interface: http://www.learnboost.com/mongoose/ ).
Express looks to still be a synchronous-oriented framework (which could just be the result of the documentation, but I did not see anything in the documentation that suggested helping write asynchronous Servers)
It really depends on your use-case. couch and redis support are pretty good. Things are still rapidly changing and there isn't a canonical way to do things ( ry has encouraged developers to specify what versions of node their code is built to work with, but if it isn't specified you should be cautious and run the tests.)
When node 0.2.0 is released, we will have a lot more stability in node-core (though things are getting there now). Until then, this is still an "edge" project and should be treated accordingly. For instance, check out the recent addition of buffers and unification of stream interfaces.
There are open-source libraries (mostly MIT and BSD licensed) for all the key things you need: cookies, sessions, serving static files, talking to DBs, templates, etc. I pieced together a web service using node-machine[1] at the core (port of WebMachine[2][3]).
There are web frameworks but it's not really much trouble to roll your own, tailored to your needs. Depends on your time budget of course. I'd love to see a high-level Rails-esque framework using node-machine, but there isn't one yet.
The irc chan on freenode is frequently populated with helpful people. The community is still small enough where everything is on the main mailing list.
Sometimes no options is better than many options.