CalcStak

A reverse-Polish-notation calculator built for the keyboard-first crowd: enter, op, done. No equals key, no parentheses, no nested expressions to babysit.

WHY RPN
If you've used an HP-12C, a Forth REPL, or any stack-based calculator, you already know: RPN is faster once your fingers know the moves. This app puts that experience on your phone without the skeuomorphic clutter.

FEATURES
• Stack display - see four levels at a glance, scroll deeper.
• Full keyboard - numeric pad, operators, and stack manipulation (swap, drop, roll, LASTX).
• Configurable angle mode (degrees / radians), stack mode (unlimited or HP-classic four-deep), and ENTER behavior.
• Storage registers (STO/RCL 0–9) for holding values across calculations.
• History - every operation, scrollable; tap a row to push that past result onto the stack. Capped at the most recent 150 entries.
• Optional Scientific pack (one-time in-app purchase): trig + inverses, log/ln, 10^x/e^x, powers, roots, π and e.
• Dark mode and a calm, monospace-forward design.
• Offline-only. No tracking, no analytics, no network calls. Your math stays on your phone.

NOT INCLUDED (BY DESIGN)
• No "infix mode." This is RPN. If that's not what you wanted, this isn't your app.
• No cloud sync. Yet.
• No ads, ever.

PRIVACY
CalcStak collects nothing. The app does not make network requests. Settings and history are stored on-device.