Is it possible to use features or some other technique to compare two sites? I have a virgin copy of Open Outreach running alongside a copy where I've made configuration changes such as site name and configurations of various modules. Is it possible to use Features or some other technique to discover and document changes I've made?
If you are using Drupal 8, yes you can. But if you are using Drupal 7 I doubt you can yet do it. There is a backport of Configuration Manager to Drupal 7, which might make it possible.

The reason I said you can't do it in Drupal 7 is that the settings are saved in database and it is very difficult to make a comparison of the databases for settings. So if you have already made the changes and don't have a log, I would suggest exporting individual features using Features Suit of Modules. 

You can checkout my presentation http://www.slideshare.net/gokulnk/features-15841090 for related Features modules which will make your work easier.

As a suggestion next time you want to keep a journal of your configuration changes please use Journal Module which should serve you well to keep track and document your changes.