"National Rail" matching MCP connectors:

Print and mail physical letters and postcards to US postal addresses, plus address verification. Upload PDF/HTML/Markdown/text/DOCX/image documents, get a quote, and pay per call with x402 USDC on Base mainnet or credit card. Supports certified/registered mail with proof of delivery and mail-merge templates.

Agentic rails for complex workflows with receipts, fees, and MCP tool access.

Self-facilitated x402/MCP payments for hosted endpoints, rail proofs, receipts, and agents.

Romania e-Factura invoices for AI agents: build UBL 2.1 CIUS-RO, upload to ANAF/SPV, query.

PaymentOracle — ES256K-signed receipts for x402 payments on USDC+EURC (Base) and XRP+RLUSD (XRPL).

Dual-rail 402 (x402 + MPP Tempo) MCP server