Keyboard Maestro just had a big update, so obviously I had to download it and become a geek (complete with latte at Air-side) to kick the tires.
I already use Alfred and Hazel and TextExpander, and although Hazel's awesomeness would be difficult to replicate, I think Keyboard Maestro could probably substitute for the other two. The jury is out. It has a lot of tires to kick, but I look for the tires that let me do stuff I haven't otherwise figured out how to do.
Notably. I have a MacBook Air. Most of my stuff fits on it with the notable exception of a large video library that lives on an external hard drive. I have other peripherals that I rarely plug in so I don't need their little helper elves running in the background all the time.
Some of this is simple enough with the provided triggers and actions: they've made it very easy to work with USB peripherals UNLESS they're mounted external drives. I immediately figured out, for example, how to start up my ScanSnap software when I plug the scanner in and then quit the software when I close and unplug it, and similar with printers and such.
But my heart's deepest desire ever since I started keeping media on external drives has been an automatic way to mount and unmount drives (Jettison solved a big part of that by just ejecting everything when I close the lid and then mounting it again when I open the lid). Most immediately I wanted a way to mount my Movies drive when iTunes loads and unmount it when iTunes quits.
It's easy enough to accomplish launching software when you plug in a drive. The converse, not so much. KM gives you no easy way to interact with unmounting drives. But there are scripts! In case anyone else has this pressing need (NEED! NEED!), I offer up my solution to ejecting the Movies drive when I quit iTunes.