Here are some advent and holiday calendars for 2023:

• Web Performance Calendar – The speed geek’s favorite time of the year
• Advent of Code 2023
• Perl Advent Calendar 2023
• Lean UXmas 2023 – The top articles from 2022’s Agile & Lean UX News
• It's a Shape Christmas | Digital Advent Calendar

There is one in French:

• 24 jours de web : Le calendrier de l'avent des gens qui font le web d'après

If you know any interesting holiday or advent calendars, please post them in the comments.