Acousterr Guitar Tuner is a free and lightweight Android app developed by acousterr.com. This versatile chromatic tuner has a size of under 3MB and is free of obtrusive ads. It takes your microphone input and shows a meter to help you tune your instrument correctly. This app supports customized tuning, which means you can easily change the tuning of any string. It also supports ukulele, bass guitar, mandolin, and electric and acoustic guitar tuning all in one single application.

This tuner displays a green light when a string is tuned correctly, and the screen doesn't time-out and sleep while tuning. It shows you which strings are already tuned and which ones are pending. The app is very responsive, snappy, and lightweight, and it works well on all Android versions, even for low-end devices. The graphics are not overly complicated, so it won't slow down your phone. Additionally, it accurately mentions the frequencies of notes, making it easy to understand the mathematics behind music.