The Feynman Lectures on Physics: Now, anyone with internet access and a web browser can enjoy reading a high quality up-to-date copy of Feynman's legendary lectures.
3Blue1Brown: is some combination of math and entertainment, depending on your disposition.
Minute Physics: simply put: cool physics and other sweet science.
HyperPhysics: is an educational website about physics topics.
MathInsight: this web site contains both narrative pages and interactive applets focusing on the concepts underlying a few topics in mathematics.
Physics with Elliot: intermediate level videos explaining a range of physics topics.
Mathologer: Enter the world of the Mathologer for really accessible explanations of hard and beautiful math(s)
Hackmath - Complex Number Calculator: This calculator does basic arithmetic on complex numbers and evaluates expressions in the set of complex numbers. It also converts a complex number into angle notation (phasor notation), exponential, or polar coordinates (magnitude and angle).
GeoGebra: Free digital tools for class activities, graphing, geometry, collaborative whiteboard and more.
StoryofMathematics: Mathematics tells a story that so few other things can tell – you can clearly trace its history throughout different civilizations, major world events, progress, war, and more. It is technical, artistic, challenging, and comforting to so many. The Story of Mathematics is the story of the world.
Probability and Statistics
StatQuest: StatQuest is a collection of videos to explain statistics stripping away the terminology and communicate the concepts using pictures.
Circuits Simulators
LTSpice: high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
Multisim: is an electronic schematic capture and simulation program.
EveryCircuit: easy to use, highly interactive circuit simulator and schematic capture tool.
LogiSim: is an educational tool for designing and simulating digital logic circuits.
Online Courses
Real Analog: is a comprehensive collection of free educational materials that seamlessly blend hands-on design projects with theoretical concepts and circuit analysis techniques.
Engineering University Program: Analog Devices is as passionate about educating the next generation of young circuit design engineers as it is about pioneering the next technological breakthroughs. The University Program is a platform where Analog Devices, working with leading educational institutions has created and deployed new hands on learning tools for the next generation of design engineers.
PredictableDesigns: Helping entrepreneurs, startups, makers, inventors, & small companies develop electronic hardware products in a predictable fashion is our goal.
Programming Languages
OnlineGDB: Online compiler and debugger for C/C++ (Free)
MatLab OnRamp: quickly learn the essentials of MATLAB.
Simulink OnRamp: learn to create, edit, and troubleshoot Simulink models.
Octave: is a free software featuring a high-level programming language, primarily intended for numerical computations, using a language that is mostly compatible with MATLAB
Mathcad: math software that lets you perform, analyze, document and share your calculations easily.
PCB Design
KiCad: A Cross Platform and Open Source Electronics Design Automation Suite.
VLSI Design
Electric: computer-aided design system for electrical circuits. It is primarily intended for integrated-circuit layout, but it also handles schematics and even textual hardware description languages.