Capo is described as 'revolutionary tool for all musicians who want to get better at playing the music they love!' and is an app in the Audio & Music category. There are more than 10 alternatives to Capo for a variety of platforms, including Windows, Mac, Linux, iPhone and iPad. The best alternative is Sonic Visualiser, which is both free and Open Source. Other great apps like Capo are Transcribe! (Paid), Chordify (Freemium), Amazing Slow Downer (Freemium) and AnthemScore (Paid).
Change the speed of the music - from 20% (one fifth speed) to 200% (double speed) without changing the pitch. Wrong key? Change the pitch in semi-tones - at full or changed speed. Out of tune? Adjust the pitch in cents (100ths of a semi-tone) to suit your instrument.