AfterShip - AfterShip is the shipment tracking API for ecommerce businesses and marketplaces.
17track - All-in-one package tracking
PostTrack.com - Universal Parcel Tracking System
Parcel - Blazing fast, zero configuration web application bundler
Instant Parcels - Package & Delivery Tracker.
WISMOlabs - WISMOlabs Post-Purchase Experience, Communication, and Marketing platform helps businesses generate more revenue by turning tracking into revenue, reduce customer friction by always keeping your customers in the know through your brand's voice.