Sejong Korean was developed by the King Sejong Institute Foundation in Korea. Their free, high-quality textbooks, mobile apps, YouTube channel, and comics are all excellent supplementary materials for your Korean studies. Unfortunately, the website has some navigation issues that cause some frustration.
Sejong Korean’s mobile apps cover beginner, intermediate, and advanced levels on the topics of grammar, conversation, news, and pronunciation. Additionally, the website has many Korean comics with English translations on the side. These offer insight into Korean culture from Korean and non-Korean points of view. There is also a video section with embedded Korean YouTube videos that include game shows, K-Pop songs, and interviews.
You can check out the three dozen high-quality textbooks with downloadable audio files available for free on the website. These cover speaking, writing, listening, and reading. Unfortunately, the books must be read online on a finicky interface.
You may want to avoid the course section, as these courses are not easy to navigate on the website. You are probably better off following the lessons on their YouTube channel instead. Additionally, although they offer ‘beginner’ courses, these are only for students who have a solid foundation of basic Korean.
Overall, Sejong Korean’s website may be frustrating to navigate, but the individual resources are worth the effort.