Xslimmer

Xslimmer is a very useful application. It does what it says on the tin, "Your Mac, on a Diet"

How it works
It works by you giving it .app files and then locates parts that aren't needed by you're system (other languages and other binaries). This then reduces the size of the applications drastically (varies). Some applications are banned because the applications think they have been patched (anti-piracy stuff).