Mac OS X: HomeControl is a free, customisable web app that lets you control your Mac from your iOS device, giving you free reign over your machine from the palm of your hand.
HomeControl is what happens when someone with an iPhone, some coding chops and the need for a customisable computer remote gets a little carried away. Brett Terpstra's created a really awesome web app that you can install on your local machine and access with your iOS device. It'll let you control all sorts of features in iTunes, adjust the system volume and launch any application in your Applications folder. It makes use of AppleScript, so it also serves as an example for many other functions. If AppleScript can do it, chances are you can add it to HomeControl.
Brett's detailed overview explains how you can edit all sorts of options by just editing a little HTML. To give you an idea, here's how easy it is to add new apps.
Just copy and paste on the the list items in the app section and change the name of the app to the app you want to launch. That'll turn this code...
...into this application toggling interface:
HomeControl is free and requires Mac OS X. You'll need to enable the built-in web server and PHP as well, but it's very easy to do and explained clearly in the HomeControl instructions. It'll take you five minutes to set up, and you'll be glad you did.
HomeControl: Local Mac Control for iPhone [Brett Terpstra]