Remindian is a macOS menu bar application that synchronizes tasks between Obsidian (as the source of truth) and various task management systems including Apple Reminders, Things 3, Todoist, TickTick, Asana, Linear, and Calendar Feed. The app allows users to configure multiple sync profiles, each connecting a source (Obsidian Vault, TaskNotes, or Generic Markdown) to a destination task service. It runs in the background with manual or scheduled synchronization, provides UI for configuration and monitoring, and includes safety features like automatic backups before file modifications, audit logging, and conflict resolution where Obsidian always wins as the source of truth. The architecture follows a layered pattern with SwiftUI for the presentation layer, a service layer for platform-specific integrations, a model layer for data structures, and protocol-based abstractions (TaskSource/TaskDestination) that enable pluggable implementations. The SyncManager acts as the central coordinator, while the SyncEngine orchestrates the synchronization process. Key features include bidirectional sync with configurable directions, duplicate detection, natural language task entry, and extensive customization options for field mapping and filtering. The application demonstrates strong engineering practices with a comprehensive test suite, careful attention to data integrity through surgical file edits and backup systems, and thoughtful handling of platform-specific integrations. While deeply integrated with macOS and specific task services, it maintains clean separation of concerns through its protocol-oriented design, making core components potentially reusable in other synchronization contexts.