Niklas Luhmann-Archiv

Luhmann was famous for his extensive use of the "slip box" or Zettelkasten note-taking method. He built up a zettelkasten of some 90,000 index cards for his research, and credited it with making his extraordinarily prolific writing possible. It was digitized and made available online in 2019

Mines, from Simon Tatham's Portable Puzzle Collection

The first square you open is guaranteed to be safe, and (by default) you are guaranteed to be able to solve the whole grid by deduction rather than guesswork. (Deductions may require you to think about the total number of mines.)

A simple way to manage your household budget with Common Lisp and TravisCI

A cool hack