Matchering

Matchering is an open-source tool by developer Sergree that masters your track to match a reference song you choose, aligning RMS, frequency response, peak level and stereo width. You give it your mix and a commercial track you like, and it returns a master with a similar tonal balance and loudness. It runs as a Python library or through a web app and Docker image, and it's the engine inside several free online mastering sites. It's simple and surprisingly effective, though a reference match is only as good as the reference you pick.