Neuron is a tiny library that aims to simplify image classification, it aims to provide the simplest tool to develop machine learning model using cutting-edge technology
TheoremJS is a mathematical framework that is packed up with tons of useful mathematical functions. It is composed of functions in most mathematical fields such as algebra, number theory, statistics, etc... It was designed to fit your need, whatever you are trying to do.
CrypTools is an organization that teaches cryptography. Their platform called learn was designed to help students or hobbyists what is the concept of cryptography by completing some challenges
The challenges can be done with or without code and the amount skills required to complete them constantly increase as you complete more and more challenges