1. Music theory content from Open Music Theory Textbook is licensed by Creative Commons BY-SA 4.0.
2. Piano lesson content from Piano Playing With Piano Questions Answered is licensed by Project Gutenberg License. Copyright © 1909 by Doubleday, Page and Company; renewed 1937 by J. Hofmann. © 1908 by McClure Company; renewed 1936 by J. Hofmann. © 1920 by Theodore Presser Company; renewed 1947 by Josef Hofmann.
3. Fluid (R3) SoundFont from Frank Wen is licensed by the MIT license
4. The MIDI files from Mutopia are licensed by Creative Commons licenses.
5. The MIDI files from Bernd Krueger are licensed by cc-by-sa Germany License.
6. Icons made by Darius Dan, Egor Rumyantsev, Eucalyp, Freepik, itim2101, mynamepong, pongsakornRed, smalllikeart, surang, Vectors Market, wanicon from www.flaticon.com are licensed by Creative Commons BY 3.0.