XO Wave is a free audio editor and sequencer and DAW plugin developed by XO Audio. Compatible OS(s): macOS, Linux.
XO Wave is a digital audio workstation designed to meet the needs of audio and video professionals, with a focus on CD Mastering and audio for video related work. It has support for direct recording from any core-audio device, importing and exporting files in a variety of formats (including songs from iTunes playlists), CD Burning, multi-track editing, and QuickTime synchronization and export.
XO Wave Open on Linux is free. XO Wave on Mac OS X comes in two versions: Free and Pro. Pro adds features such as AU support and CD burns.
A comparison of the available versions is available here.