The first one is edx.org
In May of 2012, scientists from Harvard and MIT established edx.
The first edx course on circuits and electronics from MIT was taught by Jerry Sussman, Anant Agarwal, Chris Turman, and Pyotr Mitros.
It attracted 155,000 students from 162 countries.
They joined forces with Stanford in 2013, and by June of that year, they had reached 1,000,000 students.
2nd is Allison.com
Allison is an Irish higher education online platform offering certified diploma and certificate programs.
It was established in Galway, Ireland on April 21st, 2007 by Irish social entrepreneur Mike Ferrick.
The UK's organization for Ongoing Professional Development, CPD UK, has recognized the courses.
You can find their free online courses for for all fields.
This is a great platform to start your career.
Third one is Codeacademy.COM.
Free coding lessons are available in 12 different programming languages, including Python, Java, Go, JavaScript, Ruby, SQL, CC and Swift, in addition to the markup languages HTML and CSS on the American online interactive platform Code Academy.
Code Academy's fundamental core catalog of courses is included in Free Basic Accounts.
Courses marked as free course in our course catalog are ones where you can access the lessons without a subscription.
Udacity.com
Massive Open Online Courses are provided by Udacity Incorporated, an American for profit educational company started by Sebastian Thrun, David Stevens and Mike Sakulski.
Throng claims that the company's intention to be de audacious for you, the student, is where the name Udacity originated.
KhanAcademy.Org
Sal Khan founded the nonprofit American educational organization Khan Academy in 2006.
The creation of a collection of web resources to aid in student education is its aim.
The company creates quick video tutorials.
Its website also offers additional practice questions and resources for teachers.
Expert created Khan Academy's collection of reliable, standards aligned practice and lessons.
Includes classes in language, physics, history, et cetera.
All of it is free for educators and students.