If you like puzzles, problems of the day, or lifelong learning in the math and science realms, the website https://brilliant.org/  and accompanying app are worth a look. There are several levels of membership. There is a free course level where one can do lessons in the areas like

  • Logic
  • Computer and Science Fundamentals
  • Artificial Networks
  • Mathematical Fundamentals
  • Number Theory
  • Logic
  • Science Essentials
  • Geometry Fundamentals
  • Physics of the Everyday
  • Probability
  • Games of Chance
  • Statistics
  • Group Theory
  • Differential Equations

MANY MORE: This level also gives you access to two problems of the day and several days’ worth of archived problems. There are also monthly or annual memberships that give open access to the archive and to more lessons than the free version allows.

This is worth a look just for the problems of the day.