Cadenza ($1) has a different type of display. Instead of a needle, it has two triangles that align when you're at the right frequency. It doesn't display much else, though, other than a simple scale of the number of cents that you're flat or sharp. The bottom triangle moves around a bit, even when I play a tuning fork, and there's no sort of indication, other than the alignment, that you've reached the correct frequency.
You can adjust the pitch from 410Hz to 450Hz, which is, perhaps, limited if you want to use this for an instrument playing baroque music, which could be at 392Hz. But it also has a metronome, solfège notation, and an in-app purchase lets you upgrade to features such as a sequencer, pitch pipe and more.
The $4 insTuner — Chromatic Tuner with Tone Generator (or its free Lite version) has a slick interface, and gives feedback with a needle in a circular dial. It's a chromatic tuner, and can tune to any note, but the pro version also has a strobe tuner, a spectrum analyzer, and more. Its display shows the frequencies of your notes and how many cents you are from the target, and the color of the note changes from red to yellow to green as you approach the correct frequency. It also has a tone generator, and you can change the pitch to any frequency.
In addition, it works with bowed instruments, and offers a couple dozen temperaments, such as Meantone, Werkmeister, and others. It is by far the most complete tuner app I looked at. Depending on your usage, some of the features may be overkill, but if you know what they mean, then you may need them.
Finally, Guitar Tuna (free) takes a different approach from the other apps I looked it. Its display looks a bit like an electrocardiogram, and it shows the variations in pitch on a sliding "piece of paper." When you get the note right, it pings, and a button flashes for that string. At first, I found the display annoying, but it's actually easier to use than many of the other apps. If you only need to tune a guitar, the free version will do the trick, but in-app purchases let you unlock access to other instruments.
As you can see, there are guitar tuner apps for everyone. Depending on your needs, you may be happy with a limited, free app, or you may want to get one of the more powerful tools. It's good to know how to tune from one note — and then tune your other strings to it — but it's a lot quicker to tune with an app.
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