Other Developer Advent Calendars!

If you know of other 2021 Advent calendars that belongs here, let me know and I'll get them listed here!

🎄🎄🎄Smashing Magazine published a huge round-up of Advent Calendars For Web Designers And Developers (December 2021 Edition)!🎄🎄🎄

• F# Calendar - the inspiration for this site and a tradition that started in 2010 continues!
• Advent of Code - an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language
• Festive Tech Calendar - "lots of new content from different communities and people around the globe"
• .NET Advent Calendar
• Go Advent Calendar
• The Dev Advent Calendar (from Marc Backes)
• Advent of JavaScript includes 24 challenges (you can purchase solutions)
• Advent of CSS includes 24 challenges (you can purchase solutions)
• 24 Pull Requests - "Giving back to open source for the holidays"