[bitwize]

I worked on QRes (airline reservation system) while a contractor at ITA after it had been eaten by El Goog, but before it had been fully digested. It was really neat. It was written in Common Lisp, but that's not what made it cool other than in a superficial I-like-Lisp sense. But it was written by old Lisp wizards, and their meticulous attention to detail, including maintainability. It took just a couple of M-. in Emacs/SLIME to find what I was looking for and everything was structured clearly and easy to maintain/change.

And the testing! It came with its own testing DSL that allowed you to specify templates of expected XML results and check that the actual response from the live web service matched the template. A new test could be written in a handful of lines. The test suite was HUGE and comprehensive, and when adding a new test it was easy to find a group of similar tests to put it in. I never enjoyed writing test code as much as I did on that project, and that's how it should be for every project.