We have created an shipping software that you can easily add your shipping accounts to from Stamp.com, UPS and Fedex. You can add multiple accounts from each carrier and rate shop each account.
If you have one UPS account that has special rates for heavy items and another general use account, we can rate shop between both ups account and show rates from both so you can choose the best rate.
Integrated Carriers
UPS, FedEx, USPS (via stamps.com)