DHL PHP SDK is an unofficial resource that wraps some of the DHL SOAP API's functions, including shipment and label creation. Even though the SDK is unofficial, developers still need a DHL developer account (and possibly a DHL Intraship Account) to use the API.
Who needs a tracking service when you can just hop on the USPS, FedEx, UPS, or DHL website (or whoever your carrier is) and just track? Maybe you. The Trackthis API integrates an amazing array of functions into your application. The API webpage lists over 10 carriers you can get notifications for.