MacResearch has posted a nice two part tutorial on using Platypus, a neat utility that allows you to "create native, flawlessly integrated Mac OS X applications from interpreted scripts." This include shell scripts, Perl, Ruby, Python, etc. With Platypus you can turn command-line only tools into full fledged, free-standing Mac applications that support drag and drop and even basic graphical feedback. Obviously this isn't going to make for a full GUI application, but it will allow you easily to create self-contained OS X applications that you can double-click to run. Especially for those in the science fields, and even for beginning (Ruby) script programmers like myself, Platypus makes it possible to get basic (and even not so basic) Mac app up and running very quickly.
Platypus is a free download from Sveinbjorn Thordarson, and donations are requested.
Update: fixed headline