Everyone should have this app. Where else do you get to try out a vintage-sounding synth? Apple's GarageBand turns your device into a recording studio. You can play around with unconventional instruments, funky beats and song arrangements. Fun, brilliant, and well worth the price.
Available: iOS - HK$38 (Free with fewer instruments)
Shazam is great, but it doesn't identify songs when they're hummed or sung. Sometimes you have a song in your head that you can't place, or need to know what that catchy song in a shop is. SoundHound takes a sample of the tune - whether it's the actual recorded track or you humming the melody - and tries to match it to a title in the app's massive database. That is, unless you're a really, really bad singer.
Available: iOS - HK$53, Android - Free
Old, but still so good. Everyone loves the iOS Photo Booth app, but Face Melter takes things to a whole new level. Create an infinite number of funny facial expressions out of pictures of your family and friends. Flip a frown into a grin, magnify eyes or give someone a wiggly nose. Pretty quickly you'll see why this is one of the most popular apps in the world.
Available: iOS - HK$15, but "Lite" version is free (Try Photo Warp for Android - Free)
Did you know your phone has a magnetic field that allows it to sense the presence of metal? This app has a simple and realistic interface, and (importantly) actually works to find magnetic metals, like steel or iron. It could also be used to find that "lucky" coin your aunt always hides in the dumplings during Lunar New Year. See? Saved your life.
Available: Android/iOS - Free
This is a cool, novelty app to be used at a party or during lunch break. It shows off just how sensitive your phone's accelerometer is. It lets you measure everything that vibrates, shakes or moves, and uses the information to draw the results on a graph. It's fun and educational, and makes you look like a scientist in front of friends. Or pretend it's a lie-detector machine and see who confesses …
Available: iOS - Free (Use Vibration Meter on Android - Free)