EasyPrompt is a utility for command-line scripts. It handles prompts and default values, and also provides a testing facility for mocking out the command-line user.

Lafcadio is an object-relational mapping layer for Ruby. It lets you treat database rows like first-class Ruby objects, minimizing the amount of time you have to spend thinking about database vagaries so you can spend more time thinking about your program's logic. It also offers extensive support for unit-testing complex database logic without running cumbersome setup scripts. It currently supports MySQL and PostgreSQL.

RhizMail is a test-friendly library for sending out customized emails. This is the library we use day-to-day at http://rhizome.org, where we send out more than 100 customized emails a day