Multiple MySQL instances on Mac OS X Client or Server

A new project and a server in the basement, drove us to research how we could replicate MySQL databases of two other servers onto the one in the basement. Quest: we need multiple instances of MySQL on the server, with each its own setup. Our findings and how to set this up on Mac OS X Client (your regular desktop Mac) or Mac OS X Server (your co-located Xserve, Mac Pro or Mac Mini Server) are described on this page.