At work, I'm working on including UPS integration for our product's shopping cart. I'm currently using the documented API, which supplies WSDLs. To use this API, you need a username, password and API key (our customers who use the cart for their business will have to provide this information).
There is another (undocumented) API for calculating shipping rates at:
http://www.ups.com/using/services/rave/qcostcgi.cgi
I've noticed a lot of sites using it, but I cannot seem to find any documentation for it. It also seems to be extremely old (I think it dates from the early '00s). It doesn't perform any sort of authentication so you can use it to get a quick quote. We were thinking of using this API so that our customers can use it to get a quick quote without jumping through hoops to get a UPS username, password, and API Key. My gut feeling tells me that I probably shouldn't rely on an undocumented API that can possibly go offline any day. I've also read posts where the tool calculates rates incorrectly (compared to the documented API). I haven't verified this (plan to do that next).
I just wanted to see if anyone here knew anything about it or had any documentation for it.
UPDATE:
After a quick test, it appears that the values are incorrect. For a 150 lb. package that's shipped from Hoboken, NJ to Chandler, AZ via 2nd Day Air, the documented API reports a total cost of $622.56 whereas the CGI reports a total cost of $495.18. So there is some discrepancy.