[rm445]

Mainly research and education. MINIX is meant to be (though I haven't read the code since the first edition printed in Tanenbaum's book) a clean, simple project for students and researchers to begin hacking on easily . In this day and age, research OSes don't become mainstream ones, but MINIX could be a good target for research which would make its way to the more widespread OSes if successful.

The above is stating the obvious, so I presume you are asking about commercial/embedded use. The answer is probably similar - if you want a nice clean base to start from and want a general-purpose UNIX rather than a realtime system, and you don't need much from the userland beyond classic UNIX tools. Perhaps your work involves hacking at the system level, or you're keen on having a microkernel architecture. It's a bit niche but could be a very suitable base for an embedded project.