This is a very simple Mac OS X application that allows you to test regular expressions against sample text. It is based on the Mac OS SDK's implementation of NSRegularExpression, which is based on ICU. My problem is that, as a Rails developer, I'd grown accustomed to using Rubular, a brilliant regex testing tool. However, there are subtle differences in the syntax of regular expressions between the Mac SDK and others. This tool ensures that the expressions I enter will actually work when implemented in code.