For developers and sysadmins living in terminals, calendar management often means context-switching to bloated web interfaces or proprietary apps. Enter Caledonia – a new open-source calendar client that operates entirely via command-line or Emacs, putting calendaring back where technical users work. Announced via the developer's personal site, this tool taps into the growing demand for privacy-focused, scriptable productivity tools.

Why vdir Changes the Game

Caledonia operates on vdir directories – collections of standard .ics files synced by tools like vdirsyncer. This architecture delivers three critical advantages:

  1. Offline-first functionality: All calendar data resides locally
  2. Cloud flexibility: Sync with any CalDAV server (Nextcloud, iCloud, etc.)
  3. Privacy by default: No forced SaaS dependencies

"The vdir approach transforms calendars into plain-text datasets you can grep, version control, or back up like code," explains the project documentation. This resonates with the Unix philosophy of composable tools.

Terminal Power Features

Caledonia’s CLI supports essential operations with precision:

$ caled list  # View events
$ caled add --calendar=work \
    --start="2025-05-01 14:00" \
    --timezone="Europe/Berlin" \
    "Project Deadline"

Notable capabilities include:
- Cross-timezone events: Native handling of timezone identifiers
- UUID-based management: Robust event referencing (see example output)
- Emacs integration: Bidirectional S-expression protocol for Lisp workflows

The Bigger Trend

Caledonia arrives as tech professionals increasingly reject SaaS sprawl. It joins tools like khal (CLI) and org-mode (Emacs) in catering to users who prioritize:
- Keyboard-centric workflows
- Data ownership
- Automation via scripts

The project installs via OPAM or Nix, embracing modern package management. Configuration hinges on the CALENDAR_DIR environment variable, defaulting to ~/.calendars/.

For terminal warriors and Emacs devotees, Caledonia isn’t just another calendar – it’s declarative time management built for engineers, by engineers. As distributed work fragments timezones and privacy concerns grow, such tools transform mundane scheduling into an act of technical sovereignty.

Source: Ryan Freumh – Caledonia (Tangled, GitHub)