TunaDroid is a free, simple, and accurate chromatic tuner for guitar and other instruments. It has three modes: chromatic, quick standard tuning, and more than 40 alternative tunings, all for free. It also has a special locking feature that helps you focus on a particular note. This app supports Android 2.3+ devices and works well on recent devices. It has been successfully tested on Samsung Galaxy S2, S3, S4, Tab 10.1, Tab 2, Google Nexus 4, Sony Xperia Z, and many more. If you ever encounter any issues, the developer can be reached via email at Overall, TunaDroid is a great app for anyone looking for a free, easy-to-use, and accurate guitar tuner.