oTuner

oTuner is a free and open-source musical tuner for Windows, Windows Mobile and Pocket PC users. It lets you adjust any instrument, including guitar, bass, piano and violin.

The interface is based on a small window that automatically identifies the instrument plugged into the computer. Before attempting to fine-tune the musical device, you have to make sure that the volume bar (in the far right-side of the frame) is set to a green level, in order to avoid arrow flickering.

The program indicates flat notes to let guitarist know they have to tighten their strings until the arrows reach the central triangle. During this time, you can keep an eye on the sample frequency for reference (between 430Hz A and 450Hz A). The title bar names the note played and tells you whether the pitch is flat, sharp or exact.

oTuner uses averaging and filtering to avoid flickering in the tuner, along with KissFFT's Fast Fourier Transform and Tartini Analysis Engine to improve the UI refresh rate.

There is no installation involved, which makes the tool portable. You can drop the .exe file in a custom location on the disk or on a USB flash drive to launch it on any machine without any previous setup. It doesn't make any changes to the Windows registry, doesn't need any DLLs to run, and doesn't create extra files on the HDD.