Off The Beaten Path

Have a smart phone?
Android or iPhone? Not enough representation from the Windows phones to be included, yet.
Androids are based upon Linux.

I have may apps for musical use.
Apps that make lyric generation easier. Or composition.

I also have a background in electronic engineering so I have apps that allow me to design and test schematics.

Tools that allow me to remotely wipe my phone should I lose it...also try to locate it et cetera.

One that I find invaluable is called Screebl.
"Screebl is an application that controls your screen based on orientation."

If the phone is sitting at zero degrees or ninety degrees, it will shut off.
If it is inclined in between those two it will remain on and active.
Ingenious.
One, I never have to use a button or tap to end my session with the phone, just put it down. And two, this extends battery life significantly without much from me. The display, more often than not is the culprit when it comes to battery usage.
Neat.

Maildroid - the only mail app that works every time. Expensive but worth it, imo.

WiFi Explorer is another useful tool - it allows for a WiFi connection between you Android device and your PC.
Move, delete, rename, make a new folder, zip files - all the functions of Windows Explorer within you Android device.

mooLa is another - a checkbook. It also complies statistics so you can see where your money goes. It has a bug or two; using save and repeat will eventually make it crash. But it is far easier and intuitive to use than the others.

CamCard is great for taking a photo of a business card and integrating the info into your contacts. It also eliminates the collection of cards on your desk - the best selling point, yet.

Music?

Chordwheel - want the notes for a scale or chord? Relative? etc?
Caustic - a DAW
Band In a Box Remote

GuitarPro
GuitarTapp - 3 ring binder of songs, scrollable while you play. A teleprompter for guitarists.
Maestro - composition
Musical Note Pad - composition


Miscellaneous:
InstaPaper - allows you to  save online content for later use, offline - save an article to read when on the plane.
MyCarLocator - Set it when you leave the car and then it'll draw a map back to the car.
PocketInformant - a day planner, but the new version, number three is incompatible with my phone and the sync function leaves much to be desired.

And you thought you had beaten the rabbit holes in your path?