There are a lot of code generators, like lex/flex, bison/yacc, re2c, ragel, lemon, antlr, gperf, xxd. Maybe they don't count because they're pre-existing tools

There are a lot of code generators, like lex/flex, bison/yacc, re2c, ragel, lemon, antlr, gperf, xxd. Maybe they don't count because they're pre-existing tools, but you can see how they might have started as a one-off tool and grew from there. I've written plenty of my own, either to generate code or generate tables of data at compile time.