Ukulele Toolkit from EUM lab (US$2.99, universal) is an essential iPhone app for those who play. This handy, great-looking app offers a metronome, a tuner, chord charts and more. I've been using it for months and just love it.
This app truly is a "toolkit." The tuner function is very accurate and easy to use. To get started, pluck the string you're trying to tune. As the note plays, a meter on Ukulele Toolkit illustrates if it's flat, sharp or just right. By tuning the string up or down, you move the meter until it's perfect. You can also tap C, G, A and E string buttons to hear the pitch you're looking for.
The metronome function is fantastic and eliminates the need to have a stand-alone metronome app. A large dial lets you adjust the tempo and a play button gets it started. You can opt to have the one beat play at a higher pitch than the the others. You can also enter your own time signature, change the tone of each beat, adjusting the note value and beats per measure individually. What's really cool is that you can have the metronome play one of 13 strumming patterns, which makes it very easy to play in time.
There's also a huge library of chords available that I use all the time. It's laid out cleanly and lets you see each chord's finger positions and hear what it should sound like. Finally, you can set the app to follow tenor, soprano or baritone tuning, to mach the type of uke you have.
As I said, I've been using this app for a long time and I love it. It's definitely worth buying.