And then the biblical TempleOS which is an even more unusual suspect.
"According to Davis, God said to create the operating system with 640x480, 16 colors display and a single audio voice. The operating system was coded in a programming language developed by Davis in C/C++ called "HolyC"."
not sure why you'd want to run TempleOS on a NAS. It's an incredibly impressive piece of software from a very intelligent (and sadly, very schizophrenic) man but it's not very practical.
"According to Davis, God said to create the operating system with 640x480, 16 colors display and a single audio voice. The operating system was coded in a programming language developed by Davis in C/C++ called "HolyC"."
https://en.wikipedia.org/wiki/TempleOS
http://www.templeos.org/