GAP
GAP is a programming language for computational discrete algebra, with a focus on computational group theory and computational representation theory. It is often used as a research tool in mathematics and computer science, particularly in the areas of group theory, algebraic combinatorics, and computational algebraic geometry.
Hello, world code example:
# Several ways to do it
"Hello world!";
Print("Hello world!\n"); # No EOL appended
Display("Hello world!");
f := OutputTextUser();
WriteLine(f, "Hello world!\n");
CloseStream(f);
Popularity: Less than 1% of developers are using or have used this language.*
*According to StackOverflow's 2023 survey.
Repositories on GitHub: 4,465