TL;DR: ICFP Programming Contest starts next Friday, on July 17. It's an annual open online competition originally developed by functional programmers. It feels like an entertaining 72-hour marathon with unpredictable tasks and experience one could barely express (though participants write long write-ups describing theirs). If you haven't participated in ICFP Contest — definitely give it a try this year. Register at the website and follow on Twitter.
Unlike other competitions, to participate in ICFP Contest one gathers a team of any size. In 2019, there were teams up to 12 people with a median of 3. The team has 72 hours to crack a single task which is always unpredictable, complicated, and versatile.