Architecture Review: Cal.com Companion Apps

Cal.com Companion Apps represents a strategic unification of the scheduling experience across mobile (iOS/Android) and browser surfaces (Chrome/Edge/Firefox/Safari). Rather than building five separate native applications, the engineering team has leveraged modern cross-platform frameworks to ship a cohesive ecosystem that syncs real-time with their core infrastructure.

🛠️ The Tech Stack

The architecture behind the Companion Apps is a masterclass in code reuse and modern tooling efficiency.

• Mobile (iOS & Android): Built using Expo and React Native. This allows the team to maintain a single codebase that compiles to native binaries for both the App Store and Google Play. By choosing Expo, they bypass much of the traditional native build fatigue while retaining access to native device APIs when necessary.
• Browser Extensions: Powered by WXT (wxt.dev). This is a next-gen framework for building browser extensions that abstracts away the complexities of the manifest files and build targets for Chrome, Firefox, Safari, and Edge. It ensures a consistent experience across different browser engines.
• Core Infrastructure: The apps communicate with the battle-tested Cal.com backend:
  • Framework: Next.js (React)
  • API Layer: tRPC (end-to-end type safety)
  • Database: PostgreSQL with Prisma ORM
  • Auth: OAuth 2.0 (critical for calendar integrations)

💰 Pricing Model

Cal.com operates on a transparent Freemium model, and the Companion Apps are treated as value-add interfaces rather than separate paid products.

• Companion Apps: Free. There is no cost to download or use the mobile apps or extensions; they simply require a valid Cal.com account.
• Individuals: Free Forever. Includes unlimited bookings, calendar connections, and basic integrations.
• Teams: $15/user/month. Adds round-robin scheduling, team workflows, and removed branding.
• Enterprise: $37+/user/month. Adds SSO, SCIM, HIPAA compliance, and SLA support.

⚖️ Architect’s Verdict

Verdict: Production Ready

Is this a “Wrapper”? In the strictest sense, yes-it wraps the core Cal.com functionality. However, dismissing it as just a wrapper misses the point. This is Smart Engineering.

Instead of fragmenting their engineering resources across Swift, Kotlin, and vanilla JS for extensions, Cal.com used Expo and WXT to ship to six platforms (iOS, Android, Chrome, Firefox, Safari, Edge) simultaneously. This ensures feature parity and rapid iteration. For a B2B SaaS, this is the gold standard for expanding surface area without drowning in technical debt.

Developer Use Case

For developers, the Cal.com ecosystem offers more than just apps:

1. Embeddable “Atoms”: You can import their React components (@calcom/atoms) to build scheduling directly into your own SaaS.
2. Open Source: The entire codebase is public on GitHub, making it an excellent reference for large-scale Next.js/trpc/Prisma architectures.
3. Headless Usage: The robust API allows you to use Cal.com purely as a backend scheduling engine while you build a completely custom UI.