Tools to play with in your browser

RSA_numbers_factored/ (transpiled from RSA_numbers_factored.py, BigInt in browser)
R.html show all RSA numbers with both prime factors ≡1 (mod 4)
squares.html show square sums and diffs for RSA numbers and their prime factors
validate.html show all RSA number lengths, and do a lot of assert validations

https://hermann-sw.github.io/planar_graph_playground/
Planar graph playground

https://hermann-sw.github.io/cuboid_shortest_paths
Determine and visualize shortest paths between single point on bottom face and many points on top face of cuboid

https://hermann-sw.github.io/javascript-sphere/
Simple 3D sphere JavaScript demo

https://stamm-wilbrandt.de/GraphvizFiddle/
<GraphvizFiddle/> (online Graphviz editor&layout [based on Viz.js])

https://stamm-wilbrandt.de/en/xsl-list/peg-solitaire/
(1-player board game [browser XSLT])
It knows all solutions for 33/37/39 pegs English/French/3-3-2-2 boards.
You may choose "Cheat" link (based on 1+16+64=81GB data files on the website).
There are 2,990,375,067 good positions for French board that allow to end with single peg on target field (forum link).
Instructions on how to revert a move can be found just above that posting (animation):

https://stamm-wilbrandt.de/xqib/
("foobar" → "ɹɐqooɟ" [browser XQuery])

https://stamm-wilbrandt.de/en/xsl-list/n-queens/n-queens.xsl.xml
(n-queens, 4 ≤ n ≤ 9 [browser XSLT])

https://stamm-wilbrandt.de/echo-e.to.braille.html

   ⠀⠀⣀⠀⣀⣀⠀⢹⣀⠀⡀⣀⢀⡀⢀⣄⡀⢀⡀⠈⣇⡀⢀⢀⡀⢀⡀⢀⡁⢹⠈⡇⠀⣀⠀⢀⠇⣀⠀⠀⠀⠀⢀⠎⢀⠞⠉⠺⠈⢆
   ⠒⠭⣀⠀⢸⠀⡇⢸⠀⡇⢸⠀⡇⢸⠀⡇⠀⡇⢸⠀⡇⢸⠀⡏⠀⡕⢺⠀⡇⢸⠀⡇⢸⡒⢃⡜⠀⣀⠭⠒⠀⠀⢸⠀⠘⣄⠀⣠⠀⢸
   ⠀⠀⠀⠀⣸⡉⠀⠈⠉⠀⠉⠁⠉⠈⠁⠈⠁⠈⠁⠀⠉⠁⠈⠉⠀⠈⠁⠉⠉⠉⠉⠉⠀⠉⠁⠁⠀⠀⠀⠀⠀⠀⠈⢆⠀⠈⠉⠁⢀⠎