LocalSend is a free, open-source, cross-platform application for secure local file sharing over a local network without internet access. It supports Android, iOS, macOS, Windows, Linux, and a CLI, using a combination of Flutter for the UI and Rust for performance-critical networking, cryptography, and file transfer logic. The architecture is modular: a core Rust library (`packages/core`) implements the LocalSend protocol (v2/v3) with HTTP/HTTPS, multicast discovery, WebRTC, and TLS encryption; a Flutter app provides the graphical interface with state management via Refena (Redux-like) and i18n support for 50+ languages; and a separate CLI and WebRTC signaling server are also included. The app features device discovery, file/message transfer with progress tracking, PIN protection, checksum verification, quick-save, receive history, and a web share mode that allows browser-based downloads/uploads. The codebase demonstrates high craftsmanship with clean separation of concerns, extensive integration tests, and reusable patterns such as typed isolate communication, custom DNS resolution for IPv6 scoped addresses, and connection rate limiting.