Exercism teaches programming languages through small exercises and mentor feedback on submitted solutions.
LeetCode collects algorithm, database, and interview problems, with contests and company-style practice sets.
The Odin Project teaches full-stack web development through project-based lessons that move from HTML and CSS into JavaScript and backend work.
Provides clearly structured and easy-to-understand web development tutorials, containing a large number of practical examples, covering HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java.
freeCodeCamp teaches programming through projects and exercises across web development, data analysis, backend work, and ML basics.
Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML and more.