Advent Calandars

• Advent of Code: https://adventofcode.com
• Advent of SQL: https://adventofsql.com
• Advent of Cyber: https://tryhackme.com/r/christmas
• Advent of Chess: https://www.adventofchess.com
• Advent of Craft: https://github.com/advent-of-craft
• MATH+ Advent Calendar: https://www.mathekalender.de/wp
• Java Advent Calandar: https://www.javaadvent.com

Summer Calandars

• Summer of Math Exposition: https://some.3b1b.co

Other Challenges

• Project Euler: https://projecteuler.net
• Hannukkah of Data: https://hanukkah.bluebird.sh/5784
• Everybody Codes: https://everybody.codes/home
• Pi Day Contest: https://ivanr3d.com/projects/pi