WolframAlpha - WolframAlpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
Soulver - Soulver is a software application that functions as a calculator that allows you type a continuous stream of information rather than having to input data into multiple cells.
Cymath - Free Step-By-Step Solutions to algebra problems.
Numi App - Numi is a beautiful text calculator for Mac.
Photomath - Photomath is a mobile app that will give you the ability to test your equations through a simple calculator interface that will fully explain the solution in a step-by-step fashion. Read more about Photomath.
Parsify Desktop - Extendable calculator for the 21st century ⚡