Trussed is a no_std Rust library and framework for building cryptographic firmware on microcontrollers. It implements a client-service syscall architecture: applications use strongly-typed client traits such as CryptoClient, FilesystemClient, and CertificateClient to send Request enums through an interchange channel; Service::process dispatches requests to pluggable mechanism implementations or custom backends, persists keys and files across three littlefs2 filesystems (internal, external, volatile), and returns Reply enums. It is not a standalone application or CLI but an embedded component used by firmware runners such as Solo 2 and Nitrokey 3.