For software geeks, whatever your language(s) or level of ability, the annual Advent of Code puzzle challenge is a fun set of coding challenges (some challenges are quite hard, but there’s plenty for us non-experts to work on). Here’s how the “about” write-up summarizes it:
"Advent of Code is an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like. People use them as a speed contest, interview prep, company training, university coursework, practice problems, or to challenge each other. You don't need a computer science background to participate - just a little programming knowledge and some problem solving skills will get you pretty far. Nor do you need a fancy computer; every problem has a solution that completes in at most 15 seconds on ten-year-old hardware."