I would classify djb's redo as being "fun", in large part due to its high implementation terseness and conceptual elegance permitting equivalency with make whil

I would classify djb's redo as being "fun", in large part due to its high implementation terseness and conceptual elegance permitting equivalency with make while ensuring target file atomicity, proper incremental rebuilding and a highly straightforward way of expressing build dependencies/relations based purely on metadata from the file system namespace, all while being persistent and driven solely through the shell. Build systems can be eye-opening. tup, redo, memoize.py and Bazel all demonstrate different, interesting paradigms.