Mixere is a great open-source audio application that lets you mix different audio tracks. It supports many formats including mp3, ogg and wav and can be used at parties for instance to mix the music live. It is possible to fade in, fade out of tracks, loop and auto-trigger audio and change the volume of the audio on the fly. All songs are loaded right into the main interface of Mixere with each audio file filling one track in the software. Any number of audio files can be then played simultaneously as well limited only by the operating system and sound device.
