The Mathpix Snipping Tool (available on Windows and Mac) let's you extract any LaTeX from a screenshot of an equation so you can just paste the code into your LaTeX editor. You can get it here: https://mathpix.com/

Check out this demo of the Snipping Tool on Windows. 

 

There is a software with text editing, mathematical, programming features and data visualization features called MatDeck.

https://labdeck.com/matdeck/.

A Demo version offers several interesting features such as text editing, programming in MatDeck Script and Python, flowchart drawing, 2D graphs, audio equalization using graphic equalizers, and project management. All this can be performed within the same document.

There are many examples and studies for Maths, Digital Signal Processing, Physics, Chemistry, Data Visualization, Wavelets, Data Acquisition and even Artificial Intelligence which can all be found on the website. There are user manuals available on the website.

https://www.gcemath.com

This one has multiple math calculators which provide detailed solutions to math problems : factorization calculator, sets calculator and equations calculators such as cubic, quadratic, modulus, simultaneous and linear equation solvers. For math practice, the site has quiz generators which provide detailed solutions.

H.J.Keisler "Elementary Calculus an Infinitessimal Approach"

PDF link : http:// https://www.math.wisc.edu/~keisler/keislercalc-03-07-17.pdf

https://www.bartleby.com/concepts

This page has detailed concept explainers for STEM subjects. The math concept explainers include Algebra, Geometry, Statistics, Trigonometry, Calculus, and Advanced Math. Hope this helps!