Mel,
What is your interest in CASS software? I'm familiar with most of the major vendors. Given the constant change in postal regs, rates, etc., only the big guys can seem to consistently put out a reliable CASS and presort product -- and even some of the major vendors have had problems. I don't even remember coming across an actual Fox-based CASS product, although there are a few products which offer an API you can call. A few companies are also now offering pay-per-hit components which access the postal data from their web sites.
I (as I think a few others hbave as well) built a class which passes an address to the USPS web site for correction -- although this is not "CASS Certifying" as far as USPS-approved processing necessary for presort discounts.
What specific need do you have? I can probably point you is the right direction.