Windows/Mac/Linux: Ever wanted to write a script for some repetitive task, but don't know how to code? Sikuli makes it possible for pretty much anyone to automate tasks, by telling it what to do with just some screenshots and simple commands.
If it has a GUI, you can probably use it with Sikuli. Sikuli is an open-source scripting app that uses a combination of very simple commands like click, type and wait, and screenshots to tell Sikuli what to manipulate. There's no internal API support, it just searches the screen for the image in the screenshot — meaning you can use it with pretty much anything. Seriously, the world is your oyster.
If any of that sounds at all confusing, watch the video — and if you think it's just too good to be true, try it out. They have tons of tutorials and examples of useful scripts in their documentation, as well, to get your imagination rolling. Although you've probably already thought of at least one thing you want to use this for.
Sikuli is a free download for all platforms.