It's not enough to print stamps off your printer any more. What shippers really want is what the SOAP-based Stamps.com API does: integrate that function of printing postage into your own web-based ecommerce or web hosted applications to speed up the shipment of orders out the door. With the API you can do much more than calculate postage and print stamps. You can clean addresses and track packages, among other tasks.
Postman REST Client, a powerful HTTP client that helps developers test and develop web services, has just released version 0.9.3. (Google Chrome Packaged App) which includes brand new features including OAuth 2.0 support, user accounts, bulk uploading/importing, and a brand new API Directory.