Advent Of Code
Adventofcode.com is a set of 25 computer/Christmass-themed programming challenges for 2015, 2016 and 2017.
Here are my solutions, in vanilla PHP.
Most scripts probably require at least PHP5.6, if not PHP7.
They can be run on the CLI or in the browser except that in this last case, you may sometimes run into memory limit or execution time errors (some challenges are not exactly optimized...).