Castiel Calculator

Castiel is six calculators in one: a Simple four-function calculator, a School graphing calculator with Natural Textbook Display, an Engineer workstation with a full computer algebra system, a Professional Financial calculator, and a programmable environment (Programming and Programming+) with its own programming language. Every mode shares one math engine and one editable paper tape, so you can correct any earlier line and watch everything recompute. Includes live currency conversion, receipt printing, external API support and more.

It has all functions you see in premium expensive standalone calculators, hence the name "Castiel" stands for "CASio, Texas Instruments, ELectronica" - three legendary calculator manufacturers whose ideas live in this calculator.

This is direct port of desktop application, available for Windows, MacOS and Linux. Both desktop and mobile apps support Training mode, which explains solution, not just showing you the result. Online user manual explains app operations as well as the subject, so check it out.