The XDS Compiler is a whole family of extremely good compilers for Modula-2 and Oberon-2. I know them from my DOS days, I worked a lot with them - they used to be purely commercial, now they are freeware (but not Free Software or Open Source - Free as in Free Beer, not Free Speech). There are native compilers for Windows and Linux 86 and - my personal favorite - XDS/C Compiler, which compiles Modula-2 and Oberon-2 into surprisingly readable C. Unfortunately, the XDS/C Compiler is only available for Windows and Linux 86 - an OS X version would be nice, but is unfortunately not available.