I'm looking for a commercial programming library that gives "delta
compression" support.  For example, at
http://www.proxell.com/proxell/Technology.asp the company says that
"We also have a low-level C/C++ delta compression library and API for
software developers who wish to design their own applications."
Proxell however are not answering e-mails.  I'm interested in getting
a list of all the commercially available delta compression libraries
out there.  Note that they must be commercial -- NOT open source, as
open source libraries can't be used in commercial projects.  Therefore
all code for eg. at sourceforge is out of the question.

It is for software development for windows -- therefore the component
needs to be in C++ or VB, or be able to be used in windows programming
(ie. JAVA isn't going to be useful).