Building a stock market trading game in RoR, what libraries are available?

A little searching reveals a handful of options (disclaimer: I haven't used any of these, so I can't vouch for them!).

For financial/stock data:

• yahoo_stock gem -- interface to Yahoo! Finance API
• ystock gem -- similar to above
• ruby/finance -- lots of data-fetching options

For creating charts:

• GoogleCharts gem -- interface to Google's chart API
• gchart gem -- similar to above
• rChart gem -- port of the pChart library

I would suggest some of your best places to search would be RubyGems.org and GitHub.com.

It's probably worth looking into JRuby, then you can mix Rails with any Java libraries you might need.