Founder of snapcx.io retail web services portal. At snapCX, I am building portfolio of REST style API endpoints (JSON payloads) for retail online channels. Few of services are running in production right now are

1. Shipping Tracking for USPS, UPS, DHL, FedEx
2. Address Validation and Correction (USPS engine) for USA addresses.
3. Sales Tax calculations (estimate tax, calculate tax for an order with multiple shipping buckets.)