SPDK is a library that can be used to build silent payment wallets. It builds on top of rust-silentpayments.
Whereas rust-silentpayments concerns itself with cryptography (it is essentially a wrapper around secp256k1 for some silent payments logic), SPDK can be used for more high-level operations that are required for wallets, such as scanning for payments from a chain backend, or creating and signing transactions.
SPDK is used as a backend for the silent payment wallet Dana wallet.