AfterShip - AfterShip is the shipment tracking API for ecommerce businesses and marketplaces.
Shipup - Shipup turns e-Comerce deliveries into marketing. Boost your NPC and CLV reducing your call center delivery tickets. Proven track record.
17track - All-in-one package tracking
WeSupply Labs - WeSupply Labs helps merchants provide the best post-purchase customer experience when selling online with their integrated services designed to assure a smooth post-purchase experience for end-users.
PostTrack.com - Universal Parcel Tracking System
Trackanytime - All in one Package Tracking Online Tool