Fretcetera is a musical calculator designed to assist musicians in exploring chords, scales, and progressions on various string instruments in any tuning. Unlike a traditional chord book, Fretcetera employs algorithms to compute all possible ways to play chords or scales and presents the top results based on playability. Users can customize their instrument settings to match their playing style, input personal preferences, and constraints. With the option to choose from common tunings or create custom ones, Fretcetera offers a tailored musical experience. Additionally, users can build progressions to hear chord transitions and receive suggestions based on their current chord selections.