Ask HN: What web framework/language should I learn this weekend?

So, I'm a .Net developer. I Know ASP.Net and such well and use Linux. As such, I use mono but have become a bit discontent with it recently. I don't really know any web framework other than ASP.Net, but I hope to change that.

I have a small web project I want to do in a new technology this weekend. What framework/language should I do it in? Candidates I can come up with:

  1. Ruby (and something not Rails)
  2. Go
  3. Python 
  4. Node.js
  5. Something else

What's a fun and relevant thing to develop with these days?