The boards on this site stand on work other people gave away. Here is who made what.
cm-chessboard by Stefan Haack, under the MIT license. It draws the board and takes your move by mouse or finger.
chess.js by Jeff Hlywa, under the BSD 2-Clause license. It knows the rules: what is legal, and what the position looks like after your move.
The piece drawings come from Wikimedia Commons, drawn by Colin M. L. Burnett and Rfc1394, and adapted by Stefan Haack for cm-chessboard, under CC BY-SA 3.0. If you have played chess online, you have seen them. They are the same set lichess and half the internet use.
How often a move gets played, and how the players who choose it score, come from the Lichess opening explorer, in the 1000–1400 band. Lichess publishes its data under CC0 — no permission needed, none asked. Positions are checked with python-chess before they reach a page.
The teaching is ours. We watch a lot of coaches, and we argue with most of them — but what ends up in a lesson has been rebuilt, checked move by move, and written from scratch. Ideas about chess are not owned by anyone. Code and drawings are, and those are listed above.