make
The original build automation tool — Stuart Feldman wrote it at Bell Labs 1976. Define targets, dependencies, recipes. Tabs are still mandatory.
GNU Make is the universal variant. Still the most-used build tool in the world (every Linux distro, every kernel, every C/C++ project from 1980-2010). Replaced for big projects by CMake, Bazel, Ninja — but lives on as a thin frontend (make build, make test) for everything from JS to Go to Rust projects. .PHONY is the trick everyone forgets.