ScriptMaster, by 360works.com, is pretty amazing. I'm a FileMaker developer, and I've used this in several places to extend FileMaker. Using ScriptMaster, you can run shell scripts, move/copy/create/edit/delete non-FileMaker files, run various web commands, send HTML email, modify image files, create custom dialogs, and much more. Basically, it lets you program in Java (actually, a related language Groovy) to add capability to FileMaker.
Oh, and it is free. Take a look at the cost of FileMaker plugins that do similar work and you'll be amazed. This is free because 360works.com hopes to impress people enough to buy some of their other products. I know I have - they also make SuperContainer, a great way to handle file storage for FileMaker server solutions.