Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
Oceanaudio - Ocenaudio is a cross-platform, easy to use, fast and functional audio editor.
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!
GoldWave - GoldWave. Digital Audio Editing Software. Record • Restore • Convert • Analyze. Fully loaded to do everything from the simplest recording and editing to the most sophisticated audio processing, restoration, enhancements, analysis, and conversions.