Skillshare

Skillshare is an E-learning platform which offers unlimited access to many useful courses, available for $15/month. SkillShare offers the first two months for free, and the site gives access to around 25,000 courses from the start. Whether it's fields such as graphics designing, finger painting, sound engineering, or orthodox learning like physics, biology, economics, Skillshare has got you covered.

Coursera

Offering over 2,000 different courses in about 130 specialisations, Coursera is a source of credible curated content. The content is highly self-contained which eliminates any need for outside material for mastering a skill. The certificates are priced at a range of $29-$99, but Coursera's collaboration with more than 190 companies and universities makes the certificates more widely accepted, which more than makes up for the price. Coursera offers a free trial period, during which one is free to switch courses within a specialisation and cancel a subscription at no cost.

Udemy

Udemy offers thousands of courses on 13 broad categories, while also giving online certificates upon completion of courses. Unlike Skillshare, a Udemy user must purchase each course in order to avail the learning materials. Information regarding the course costs, requirements, reviews and the detailed curriculum can be found on the Udemy site. A negative aspect of Udemy is that the quality of the courses isn't consistent, because the uploaded content (especially the free ones) aren't always curated.

EdX

Created by Harvard and MIT, EdX currently offers around 1,250 courses along with 20 micro-masters courses, which a number of colleges may accept. Backed up by instructor expertise and splendid reviews, EdX has been a game changer for students and job-seekers, despite the high cost of some courses (prices range from $50 to $300).