Free tier
Simple and School, and the paper tape, are free with no time limit. The advanced modes run on a per-session timer until you buy, but the trial itself never expires - no card and no account needed to try them, for as long as you like.
Free to try
Get Castiel
The same engine and the same tape on every device. Simple and School are free to use, with no time limit. The advanced modes - Financial, Engineer, and Programming - run free for a session before stepping back; a small payment on most platforms removes that limit, and the Linux build is free in full. No ads, and no account to create.
i
The Microsoft Store edition and Linux editions are available today, the Android build is in open testing, and the Watch build is in closed testing. Apple builds are ready, but not published yet - this page will list each one as it ships.
Desktop
Windows
The full instrument on Windows: every mode, the side panels, and the docked editable tape. Available now on the Microsoft Store. The trial never expires - you can keep using it for as long as you like, and the one-time $2 purchase is there when you want to remove the session limit on the advanced modes.
Get it from Microsoft StoreMSI installer
macOS
The full instrument on macOS, with every mode and the docked tape. Arriving on the Mac App Store. Coming soon.
Mac App Store
Mobile
Android
The same engine in your pocket, with a swipe-up tape drawer. Now in open testing on Google Play and free to join - there is no tester group and no invitation any more. Open the Play listing on your phone and install, or opt in from a browser first. Every mode is unlocked during testing; later the modes above School will need a one-time $2 purchase, while Simple and School stay free.
iOS
Castiel for iPhone and iPad, carrying the same modes and the same tape. Arriving on the App Store. Coming soon.
App Store
Watch
WearOS Watch
Simple mode on your wrist, for a quick sum away from the desk. Still in closed testing. Joining takes two steps and is free: first join the tester group [email protected] (membership is automatic), then open the Google Play test link and install.
One small payment
A single small payment removes the session timer on most platforms - Linux already ships the full app for free. There are no ads on any platform; pricing and payment terms vary slightly by platform - see below for details.
Your data stays yours
Calculations, saved tapes, and settings live on your device. Connectors for currency rates or an AI provider are opt-in and use your own keys.
Prefer nothing to install?
A browser version of Castiel is under development. It is not available yet - see the web app page for what is planned.