Google is your friend. Googling free cobol returns about 1,810,000 hits and one of the first is http://www.freebyte.com/programming/cobol/ which talks about a number of free COBOL compilers that you can install on your PC (maybe some on the MAC as well). I have used GnuCOBOL (previously OpenCOBOL) and it is quite good at replicating z/OS Enterprise COBOL.