The url for the site is http://www.aptcomp.com but there is no mention of OS/2.
I have downloaded it again and tried it. It starts okay but I have not tried creating/printing an envelope with it or labels.
I have used StarOffice for OS/2 to create labels and even business cards but had no real success with envelopes (perhaps it was due to my printer - a HP Deskjet 400 - wearing out since I had it for awhile).
OS/2 Warp-ed to the very end.