Codecademy seems good if you wish to learn many programming languages in a short time and becomes a pro. But to become a codecademy pro, you need to pay up.
I like MIT OpenCourseWare the most because everything is free. I could online 'sit in' their lecture halls, 'join in' the classes and tutorials. I am glad to have learned Python and many other engineering things 'when I was in MIT'.
I also like edX where also everything is free. Again 'when I was in Harvard', I attended many lectures outside engineering. The rock star I admire most is Michael Sandel. I remember vividly I once sat in Harvard's huge lecture hall and very excitedly felt that I was a real, non fake Harvard man.
MIT OpenCourseWare - Wikipedia
MIT OpenCourseWare (MIT OCW) is an initiative of the Massachusetts Institute of Technology (MIT) to publish all of the educational materials from its undergraduate – and graduate-level courses online, freely and openly available to anyone, anywhere.
MIT OpenCourseWare is a large-scale, web-based publication of MIT course materials. The project was announced on April 4, 2001 and uses Creative Commons Attribution-Noncommercial-Share Alike license.
The program was originally funded by the William and Flora Hewlett Foundation, the Andrew W. Mellon Foundation, and MIT. Currently, MIT OpenCourseWare is supported by MIT, corporate underwriting, major gifts, and donations from site visitors.
The initiative has inspired more than 250 other institutions to make their course materials available as open educational resources through the Open Education Consortium.
As of May 2018, over 2,400 courses were available online. While a few of these were limited to chronological reading lists and discussion topics, a majority provided homework problems and exams (often with solutions) and lecture notes. Some courses also included interactive web demonstrations in Java, complete textbooks written by MIT professors, and streaming video lectures.
As of May 2018, 100 courses included complete video lectures. The videos were available in streaming mode, but could also be downloaded for viewing offline. All video and audio files were also available from YouTube, iTunes U and the Internet Archive.
edX - Wikipedia
edX is a massive open online course (MOOC) provider. It hosts online university-level courses in a wide range of disciplines to a worldwide student body, including some courses at no charge. It also conducts research into learning based on how people use its platform. EdX is a nonprofit organization and runs on the free Open edX open-source software platform.
The Massachusetts Institute of Technology and Harvard University created edX in May 2012. More than 70 schools, nonprofit organizations, and corporations offer or plan to offer courses on the edX website. As of 29 December 2017, edX has around 14 million students taking more than 1,800 courses online.
Coursera - Wikipedia
Coursera is an online learning platform founded by Stanford professors Andrew Ng and Daphne Koller that offers courses, specializations, and degrees.
Coursera works with universities and other organizations to offer online courses, specializations, and degrees in a variety of subjects, such as engineering, humanities, medicine, biology, social sciences, mathematics, business, computer science, digital marketing, data science, and others.
As of June 2018, Coursera had more than 33 million registered users and more than 2,400 courses.
Codecademy - Wikipedia
Udacity - Wikipedia
Udacity is a for-profit educational organization founded by Sebastian Thrun, David Stavens, and Mike Sokolsky offering massive open online courses (MOOCs)
According to Thrun, the origin of the name Udacity comes from the company's desire to be "audacious for you, the student". While it originally focused on offering university-style courses, it now focuses more on vocational courses for professionals.