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.
Read more: https://adventofcode.com/2021/about
Problems will appear here: https://adventofcode.com/2021
Previous years: https://adventofcode.com/2021/events
Posting it here because a lot of people might not know about this.