Castiel
Castiel: A broad free calculator suite, with a one-time Windows upgrade to remove advanced-mode limits. Ranked #10 of 32 in Scientific Calculator Apps by our editors (7.6/10); pricing: Free plan · paid from $2; best for users wanting an inexpensive all-in-one calculator.
At a glance
- Editor score7.6 / 10
- PricingFree plan · paid from $2
- Best forUsers wanting an inexpensive all-in-one calculator
- Free planYes
- Paid from$2 one-time
- Platform supportCross-platform
- Facts checked28 Sep 2026
Where it wins
- Free Simple and School modes include unlimited arithmetic and scientific calculation.
- Advanced tools span graphing, equations, matrices, statistics, and computer algebra.
- An editable paper tape recomputes dependent results across modes.
Where it doesn't
- Advanced modes in the free tier are limited to about 30 minutes per session.
- The listed one-time $2 full-version purchase is for Windows.
- Android is in open testing, while Apple releases are pending.
Our verdict on Castiel
Castiel brings several calculator modes together for students, professionals, and everyday users who want more than a basic scientific calculator. Simple and School modes offer free, unlimited arithmetic and scientific calculation, with natural textbook entry and exact or decimal results. The broader toolset includes graphing and 3D surfaces, equation and inequality solving, statistics, spreadsheets, computer algebra, numerical methods, matrices, vectors, units, and constants. Financial mode covers cash-flow and time-value calculations, while Programming mode supports reusable Catena sequences. It is a wide-ranging option for people who want these capabilities in one calculator rather than a focused app for a single task.
The free tier is useful for ongoing basic work, but it places a session limit of about 30 minutes on advanced modes. The full Windows version is a one-time $2 purchase and removes that timer. The published plans therefore make the choice straightforward: occasional or basic users can stay with the free modes, while frequent users of advanced features may prefer the paid Windows version. That purchase is specifically listed for Windows, so the same upgrade terms should not be assumed across other platforms.
Platform availability is an important consideration. Windows and Linux releases are available, while Android is in open testing; Apple releases are pending. An editable paper tape is shared across modes and recomputes dependent results, which can help when changing an earlier value in a calculation. Programming sequences can be created through recorder, blocks, and text views, with an AI assistant available to help draft them. Castiel suits buyers seeking broad scientific, financial, and programming tools at low cost, particularly on Windows. It is less suitable for someone who needs unrestricted advanced sessions without paying, or who requires an already released Apple app.
Castiel pricing
All 2 Castiel plans and prices →
Castiel fact sheet
| Free plan | Yes |
|---|---|
| Paid from | $2 one-time |
| Platform support | Cross-platform |
| Equation solving | Yes |
| Statistics tools | Yes |
| Programmable functions | Yes |
| Complex numbers | Yes |
| Offline mode | Yes |
| Matrix operations | Yes |
| Deployment | Desktop, Mobile |
| Platforms | Windows, Linux, Android |
| Compliance & security | GDPR |
| Built for | Solo, Small business, Mid-market (editorial estimate) |
| Pricing | Free plan · paid from $2 (source) |
| Website | castiel.dmkilab.com |
| Facts checked | 28 Sep 2026 |
Alternatives to Castiel
- Wolfram|AlphaBroad computational answers across math, science and more, with paid step-by-step help.9.3
- GeoGebraA broad, visual math toolkit for learners, with graphing, algebra practice, and classroom tools.9.1
- Desmos Scientific CalculatorA focused web calculator for scientific functions, lists, variables, and complex numbers.8.8
See all Castiel alternatives →
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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