This page is going to be an unstructured list of links, resources, and factoids that interest me, and will be updated every once in a while. If you spot a dead link, reach out to me and I'll try to either replace that with a working alternative or update this page to indicate what's going on.
RIES inverse symbolic calculator. It's the opposite of an equation solver/calculator: it takes in decimal approximations, and tries to find "nice" expressions that evaluate to the input, or equations that have that as a solution. Based on Robert Munafo's ries.c. For example, plugging in 0.4151707 (April 15, 1707 is Leonhard Euler's birthday) yields the approximation
Schrödinger Crosswords. These are crosswords that have multiple valid solutions. The most famous of these is probably "Election Day" by Jerry Farrell, published the day of the 1996 US presidential election. The central entry is clued as "Lead story in tomorrow's newspaper (!)", and can be filled in as either "BOB DOLE ELECTED" or "CLINTON ELECTED", and each filling leads to cohesive solutions for the rest of the clues as well! This as well as many more Schrödinger crosswords can be found here.
It's possible to make cryptic crossword that have multiple solutions as well: here's one that "predicts" the result of the Brexit referendum.
Alex Healy's Subset Anagram Finder. This is a tool for finding "subset anagrams": for example, if you feed it the list of all countries, it'll tell you that the letters of Liberia and Sudan taken together can be rearranged to get Belarus and India, and will return a list of many more such examples. I put in a list of animals, and got back that Alligator + Cobra anagrams to Cat + Boar + Gorilla. This paper explains the math behind the algorithm that makes that happen.