Rule of 3 Calculator is described as 'portable tool that allows you to apply the mathematical Rule of Three in an easier, faster and more practical way!' and is a Calculator in the Education & Reference category. There are more than 100 alternatives to Rule of 3 Calculator for a variety of platforms, including Windows, Android, Mac, Online / Web-based and iPhone. The best alternative is SpeedCrunch, which is both free and Open Source. Other great apps like Rule of 3 Calculator are Wolfram Alpha (Freemium), Qalculate! (Free, Open Source), Windows Calculator (Free, Open Source) and fxSolver (Free).
SpeedCrunch is a free, fast, high precision open source algebraic calculator with an intuitive interface and a extensive list of features, including: Unlimited Variables, Syntax Highlighting, Functions, with 'Automagic' Completion, 50 Decimal...
Wolfram Alpha is a "Computational Knowledge Engine" - different from a search engine, it answers factual queries directly by computing the answer from structured data, rather than providing a list of documents or web pages that might contain the answer.
Qalculate! is a multi-purpose cross-platform desktop calculator. It is simple to use but provides power and versatility normally reserved for complicated math packages, as well as useful tools for everyday needs (such as currency conversion and percent calculation).
A simple yet powerful calculator that includes standard, scientific, and programmer modes, as well as a unit converter. It's the perfect tool to add up a bill, convert measurements in a recipe or other project, or complete complex math, algebra, or geometry problems.
Soulver is a smart notepad with a built-in calculator. It gives instant answers to any calculations it finds in your text. It's a better way to work stuff out than with a traditional calculator, and a more lightweight tool for quick calculations than a spreadsheet.
High precision scientific calculator with full support for physical units. - Evaluation of mathematical expressions - Parsing and handling of physical units (All SI units, imperial units, time-based units, ..