One company have a object-oriented database programmed under Mumps that is so backwards compatible to the point it can interface to RS232 dumb terminals and run utilites and code from the 70's. Used very much by governments and hospitals, it's one of the most insecure platforms I've ever worked.

Bonus - perfectly valid Mumps code

  P       R I N T S (A,L)=1,(S,T)=I N G
          G I V E N A
  O       F A=L:L:S Q:U=A R E  S B=E L O W (A*A),!
  I       S (U,R,E)=T H 1 N K I T=S G O O D