Magnum Modula-2
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A Modula-2 compiler for 16 bit OS/2 and DOS, in its day considered a fairly robust compiler but came without any utilities or debugging facilities requiring you to make use of the SDK from IBM or Microsoft for the linker etc, and it did provide an interface to Microsoft's CodeView symbolic debugger as supplied with MASM.
Noticeably Magnum Modula-2 fully implemented IEEE 754 floating-point math in its libraries, one of the first to do so for any language or platform.