PayID is a protocol that connects siloed payment networks through a universal address. A PayID (e.g. alice$example.com) can map to the URL https://example.com/alice and resolve to Alice's address on an underlying payment network (e.g. bank or blockchain).
Xpring is the open developer platform for money. It offers a set of tools, services and programs that makes it easier for developers to send and receive payments in any currency, across any network, using the XRP Ledger and Interledger Protocol.