I use mk for all my personal projects. It is such a useful place to store maintenance operations on files exactly where they are needed. Not just build-type operations, but also syncing with remote stuff and other maintenance things.

My webside is managed by a big mkfile which builds html from markdown using pandoc and deploys over ssh. There is even a target in there for checking for dead links using curl.

I just counted: 778 mkfiles in my personal files.