Sp-client 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), sp-client is concerned with high-level wallet stuff, such as parsing incoming transactions, managing owned outputs, and signing transactions.
This library is used as a backend for the silent payment wallet Donation wallet.