Activitypub-federation is a high-level Rust framework for implementing ActivityPub federation. It provides abstractions for handling incoming and outgoing activities, fetching remote objects, managing HTTP signatures, and integrating with web frameworks like Actix-web and Axum. The library uses a trait-based design where users define their own data structures and implement Object, Activity, and Actor traits to plug into the federation system. It includes sophisticated features like an activity queue with exponential backoff retry logic (1 minute, 1 hour, 2.5 days), automatic caching of remote objects, and comprehensive security measures including HTTP signature verification.