USPS Informed Delivery - Get an image of your mail before it arrives
BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
PackageX - PackageX is a modern logistics platform.
Dead Link Checker - Check for broken links on any website
Shippo Package Tracking API - One API to track packages across multiple shipping carriers
LinkChecker - LinkChecker is a free, GPL licensed website validator.