As you probably already know—JavaScript is a language and the rest are all libraries and frameworks built in JavaScript (Node also has a C++ core too, but I digress). Just like Ruby is the language that Rails is built in.
The first distinction is between client-side and server-side technologies. Client-side code (e.g. Angular, Ember, Backbone, jQuery) run the in browser on the user's computer. Angular, Ember, and Backbone try—to an extent—to apply the MVC approach (like in Rails) to your JavaScript on the client in an effort to keep your code organized and DRY.
You only need one of the three. Backbone is probably the most popular. Angular, which is built by Google, also has a strong following. Ember is up and coming, but it's built by Yehuda Katz amongst others. Yehuda is a core contributor to Rails and Ember shares many of the same values (e.g. convention over configuration). In addition, it's built to play nicely with Rails. Backbone is the most minimal of the three and Angular takes an approach that expands HTML in interesting ways. It's worth dabbling in all three and seeing which one tickles your fancy. I should note that you can use any of the three with Rails. That might be a good jumping off point as you explore the world of JavaScript.
Okay, now on to the server. Node.js is a completely different beast than Rails. It's a platform, not a framework. This a bad example, but it's probably closer to Apache, Nginx, Webrick, or Mongrel than it is to Rails or Django. It basically creates a server-side JavaScript environment based on Google's V8 JavaScript engine along with some basic modules for networking and filesystem IO.
A big difference is the community. The Node community tends to favor small, modular code that can be pieced together to create bigger systems. As a result, large monolithic frameworks like Rails haven't really gain any kind of traction in the Node community. The frameworks exist, sure—Sails and Tower are two such examples, but they haven't really taken off.
The best place to start is probably Express.js, a popular but lightweight framework for Node inspired by Ruby's Sinatra. If you're not familiar with Sinatra in Ruby, play with that first (along with Ember, Backbone, or Angular) and then try Express. Express is actually a little more robust than Sinatra (for example, it includes a solution for logging—Sinatra does not).
It's also worth getting comfortable with NPM (the Node Package Manager). It's a lot like RubyGems, but with some interesting differences—for one, it keeps your modules (gems to the Rubyist) in a directory local to the project. I like to think that NPM is what RubyGems would be if RubyGems got to start over knowing it's own mistakes.
I hope this helps. Feel free to reach out to me on Twitter (same username) if you have any further questions.
I might suggest going through the learning curve this way:
- Rails + regular JS
- Rails + jquery/underscore (I'd moreso recommend jquery because everyone knows it)
-Rails + jquery + knockoutJS (it's pretty small, and does one thing, after using jquery, you should start to notice the problem it solves)
- Rails + angular (angular is complex, but by the time you string together pages with jquery and knockout, you'll start to see why you need a system like angular to really step in and handle things)
I just think it's important to experience/understand a problem before using the tools that solve it.
http://www.amazon.com/dp/0596517742
http://www.amazon.com/jQuery-Action-Second-Bear-Bibeault/dp/1935182323
http://www.alfajango.com/blog/rails-3-remote-links-and-forms/
http://www.alfajango.com/blog/rails-3-remote-links-and-forms-data-type-with-jquery/