A free (but not open) barcode generator for mac  and windows (app & library):

• Free Barcode Software for Mac and Windows – Free barcode fonts, free barcode generator, free barcode libraries, free label printing software for EAN, ISBN 10, ISBN 13, UPC, 128, 39, 2-of-5, PDF 417, Datamatrix and many more barcodes.
  What you find on this site is commercial grade barcode software that we have released into the public domain. It is unsupported but it won’t cost you a penny to use it.
  (tags: software freeware macosx barcode)