I have been looking into node and trying to understand the various components . I have tried node express . Are there other application frameworks like express ? Is there any one framework recommended ?
There are many frameworks and libraries that you could include and use. It depends on what you want to do. npm has many libraries that you can download and use with node. I would recommend at least downloading and using underscore or lodash for declarative programming. They are good to have.
There are many other cool libraries/fameworks you can try like sails.js, mean.io, and yeoman.
Express is great though. It really helps with structure and handling routes and middleware. (For example, I was able to add gzip to my respsonses with one line of middleware code). You could do it all without express, but it makes working with node.js so much easier.
If you want to use Web Sockets, use Socket.io. Web Sockets are great for real-time information. The example given is always chat, but you could use it like stack overflow when a new message, or new rep comes in. Basically something happened from another user and you want to display it without a page refresh or polling.
To handle larger volume on an "Enterprise" level, look at the Node Cluster functionality. You can create a node process per CPU processor core.
Again, it would be good for you to describe more about what you are trying to do, but you could build a web app with just node.js and express.