"OS-9 is completely structured, the source code looking much like Pascal, and is modular to an extraordinary degree."

— Dick Pountain, "Byte U.K.", Byte December 1986, p.334

"I had never played with OS-9 before and was pleasantly surprised at how nice it is to use. It provides all the better features of UNIX, like pipes, filters, and redirection (rather like a grownup version of DOS 2.0), and includes a remarkable language called BASIC09. This is to Microsoft BASIC as Robert de Niro is to Sylvester Stallone (i.e., it approaches things with rather more finesse). It's completely structured, the source code looking much like Pascal, and is modular to an extraordinary degree, global data being forbidden altogether. Individually named procedures can be separately compiled and even run and tested from the command line, then called from a main program."

— Dick Pountain, ibid.