I built Blockcore Wallet some years ago as a "crypto wallet" (also had Bitcoin support), but there is only one chain left. Though it also works well as a Nostr signer and I've used it for years now. It stores the keys encrypted, uses background process to keep the private key in-memory when unlocked. It supports multiple accounts, from recovery phrase. Also, manual import of any nsec.

Will likely soon remove all wallet features and make it a pure key manager, with support for Nostr and DID.