Tenacity
Tenacity is an easy-to-use cross-platform multitrack audio editor/recorder. A free and open source program
Audacity
Audacity – free and open source, multi-platform and easy-to-use, multi-track audio editor and recorder
LosslessCut
LosslessCut – free and open source, simple and ultra fast cross platform tool for lossless trimming/cutting of video and audio files