Alexander Bogomolny: Interactive Mathematics Miscellany and Puzzles →
Hat tip to Daniel Arovas. The link above leads to an array of links categorized by math topic and this explanation:
Back in 1996, Alexander Bogomolny started making the internet math-friendly by creating thousands of images, pages, and programs for this website, right up to his last update on July 6, 2018. Hours later on July 7th he passed away.