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.