Below is a list of some of the best Free Web Development courses available on the Web. If you're a complete beginner and want to learn Web development then these courses are a gold mine for you.
About half of these courses also offer free certificate of completion. So it could also be a great addition on your Resume. If you don't have any Computer Science background then there's a course called CS50 which will give you a very solid foundation of Programming concepts.
Here's the list of courses along with programming technologies they teach:

1. FreeCodeCamp: HTML, CSS, Javascript, React.js, Node.js, MongoDB
2. Introduction to Computer Science CS50: HTML, CSS, Python, Javascript, SQL
3. KhanAcademy - Computer Programming: HTML, CSS, Javascript, jQuery, SQL
4. The Odin Project: HTML, CSS, Javascript, Ruby, Ruby on Rails
5. Bento.io: HTML, CSS, Javascript, Python, SQL, Postgres
6. Upskill - Essential Web Development Course: Javascript, HTML, CSS, Ruby & Rails, React.js, SQL
7. Udemy - Foundations of Front-end Web Development: HTML, CSS, Javascript, jQuery, Backbone.js
8. The Gymnasium - Modern Web Design: HTML, CSS, Javascript

For more details about these courses and to know which ones offer free certificates, read this Guide on WebEmployed.