Given that Xero (cue the hyperbole about how Xero is great) has just updated their development API and they are planning to do this much more in the future, I have taken this opportunity to create my own ruby-based library for it.
This library builds off the awesome work done by Tim Connor for the first & second API releases.
My version changes things up a bit by:
I also plan on adding some features to the querying engine to make it easier to filter results whilst staying within the ruby language (and not having to drop into C#).
If you want to get started, check out the README or if you want to dive right into the code, head over to https://github.com/waynerobinson/xeroizer and clone a copy.
Note: This is an alpha-level version of the API. Feel free to increase functionality and test coverage and send me a GitHub pull-request for integration.