Chordopia

Chordopia is a chord finder app for guitar, ukulele, and mandolin. It runs on the iPhone, iPad, and iPod Touch.

Highlights

It works both ways! You can enter a chord name and Chordopia will show you chord diagrams for many different voicings of that chord. Or you can do the reverse: drag the dots in the chord diagram to different frets, and Chordopia will tell you what the new chord is called.
Sound — Chordopia not only shows you the chord diagram for each voicing, but also lets you hear how it will sound.
Supports alternate tunings such as drop-D and DADGAD, as well as arbitrary custom tunings.
Chordopia is not a fixed chord book of predefined chord diagrams. Instead, it works by searching through all possible combinations of finger positions on your instrument to find the ones that produce the chord you want, all in a fraction of a second. It then ranks them based on how easy they are to play and how good they sound, and shows you the best ones first.
Chordopia knows more than 50 chord types for each of the 12 root notes for a total of more than 600 chords, not counting variants with an out-of-chord alternate bass. The number of voicings varies by chord, instrument and tuning; for example, for a guitar in standard tuning, there are more than 100,000 distinct voicings to discover.
In addition to the built-in instruments, you can define your own custom instrument with 1 to 8 strings in any tuning.

The full help text of the app is here.

A listing of chords supported by the app, and the first four voicings of each in standard tuning, is here.

Screenshot

Chordopia is available for purchase in the App Store.

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