This page, and most of the other pages concerning LEP technology (not including weapons) have been put together into one easier to navigate article, entitled LEP Technology. I expect that this page will be deleted very soon. Thank you.
The Omnitool is most likely one of Foaly's inventions. It opens most regular locks. You can pay extra gold to get an omnitool able to short some electronic locks.
Holly Short's Omnitool was given to her by her mother, Coral Short. Mulch Diggums stole it, and therefore it caused the Hamburg Incident, as the criminal escaped and locked himself in a car. Holly re-obtained it in The Time Paradox.
Later versions of this tool can be used to make fairy phone calls. You place your middle finger in the center of the omnitool, which is on your palm. You then place your thumb beside your ear, so that you can hear what is being said, and your pinkie finger beside your mouth, so that the omnitool can pick up the sound vibrations coming from your mouth. After all this, it looks nothing more than as if you were a child talking into an imaginary phone!
We do not know of any other uses of the omnitool, but as its name suggests, there are probably plenty more to be discovered!