ColdFusion MX 7 is Macromedia's (now Adobe's) powerful server side programming language. It is easy to pick up and allows for rapid development and deployment of web applications, and best of all for us Mac users it written entirely in Java.
So what you ask? Well, that means that you can run a developer's version on your Powerbook (or Mac mini, or PowerMac, or.. well you get the idea). Sean Corfield has posted some very good instructions on how to get CFMX running on OS X (which may or may not change thanks to Tiger).