Saperle says: As a HUGE Doctor Who fan, I'm constantly on a quest for ways to find the best Sonic Screwdriver app out there-- because who looks at a phone and thinks, this could be a little more sonic?
MultiGadget Though there's nothing inherently Whovian about this app, you need it to install the next two apps (and can use it to install similar packs for Star Wars, Harry Potter, and other equally-geeky franchises you wish your phone to imitate the sounds of).
Sonic Screwdriver Gadgets This is the best of all the Sonic Screwdriver apps available in the app store right now (there used to be a better one by the same developer but it no longer exists) and has both the screwdrivers of the second Doctor, both of the Fourth, the ninth, tenth and the eleventh Doctor's. You can set the sounds as a notification sound too! It also has various recordings of the catch phrases of each of the Doctors.
Doctor Who Gadgets Much like the above app, this one has sounds and quotes from the Cybermen (with an electrocuting cyberhand and a laser gun), the Daleks (the whisk), the Master (sonic laser), River Song (sonic screwdriver), and the TARDIS.
Sonic Screwdriver This app only has one Classic Who screwdriver, as well as the most recent two, and it also has River Song's screwdriver and a Dalek arm. It also lets you zoom in on each gadget so it is the size you prefer, and change the background behind each gadget (though the selections are pretty bland).
Retro Clock Widget If you're going to be traveling in time you'll need an app that tells you what time you are actually in AND will blend in should you end up in the past.