Introduction

Musubi is a privacy-first shared calendar app for mobile. The name comes from the Japanese word 結び (musubi) — knot, bond, or connection. The idea: one place to connect your schedule with the people around you, without giving your calendar data to a third party.

You can use the hosted version at musubi.pro or run it yourself.

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How it works

Musubi is built around three core concepts: calendars, events, and invites.

Calendars are the main organisational unit. You create a calendar, give it a name and colour, and it becomes a shared space for events. You can own multiple calendars — one for family, one for a project, one for a sports team.

Events are linked into calendars rather than nested inside one. The same event can be linked to a work calendar and a personal calendar, edited once, and seen by members of both. Its home calendar controls who may edit it. Events support titles, start/end times, optional notes, location, a link, and recurrence rules (see Recurring events below).

Invites are how other people join your calendar. You generate a shareable invite link from within the app; anyone who opens it and has an account can accept and become a member.

A member’s abilities depend on their role: viewers can see events, editors can also create and edit them, and owners can additionally rename the calendar, manage members, and delete it. Ownership can be transferred to another member.

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Recurring events

Musubi supports recurring events using RFC 5545 RRULE strings. The app ships with presets (daily, weekly, weekdays, monthly, yearly) and a custom editor for more specific patterns — for example, “every Tuesday and Thursday” or “every other week on Monday, Wednesday, Friday, 10 times”.

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Real-time sync

When someone creates or updates an event, the server nudges connected members over Server-Sent Events (SSE). SSE is best-effort; reconnect and delta sync are the durable recovery path. External providers are polled on a schedule and send the same kind of refresh nudge when their mirror changes.

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Settings

A few settings worth knowing about:

• Default calendar view — choose between day, week, or month as your opening view
• Week starts on — Sunday or Monday
• Theme — system, dark, or light
• Time format — 12-hour (AM/PM) or 24-hour
• Date format — the order dates are written (D/M/Y, M/D/Y, or Y-M-D)
• Show Kanji — toggles Japanese month and day characters in the calendar header. This is purely an aesthetic touch reflecting the Japanese name and philosophy behind the app; it is not a localisation feature

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Tech stack

Layer	Technology
Mobile client	React Native (Expo SDK 56)
Routing	Expo Router — file-based navigation
State	Zustand
Calendar UI	Custom, in-app (components/cal/) — month/day/week, pinch-zoom, drag
Recurrence / dates	@musubi/calendar — logic-only package (RRULE + date helpers)
Animations	Reanimated v4 + Gesture Handler
Server	Express.js (Node.js)
Auth	Better Auth — email/password + Google/Apple
ORM	Drizzle ORM
Database	PostgreSQL
Real-time	Server-Sent Events (SSE)
Monorepo	pnpm workspaces + Turborepo

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Project structure

• Directoryapps/

  • Directoryapi/ Express API server (the backend)

    • …
  • Directoryclient/ Expo / React Native app (the frontend)

    • …
• Directorypackages/

  • Directorydb/ Drizzle schema, query modules, PostgreSQL migrations

    • …
  • Directorytypes/ Zod schemas + inferred types — the client/server contract

    • …
  • Directorycalendar/ Recurrence (RRULE) expansion + date helpers — logic only

    • …
  • Directoryauth/ Better Auth configuration

    • …
  • Directoryconfig/ Environment loading

    • …
  • Directorydocs/ This documentation site (Astro Starlight)

    • …
• turbo.json Task graph (dev/build)
• docker-compose*.yml

For a deeper, layer-by-layer tour of each workspace, see the Architecture Overview.

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Roadmap

Planned features, current priorities, and what’s in progress live on the public Musubi roadmap on GitHub.