You can learn Ancient Greek online on Tandem, or Mango Languages.
Learn Ancient Greek on Mango Languages
Mango Languages uses algorithms to offer a personalized language learning experience. Language learners can speak and hear the language they are learning, participate in daily quizzes to reinforce their progress, and even engage in live conversations with native speakers around the world. Language instructors also use Mango Languages to create customizable lessons tailored to each student's current skill level.
Tandem is a free platform with a simple premise: there is probably someone out there who is learning your native language, and whose native language you want to learn. So they put you in touch with them.
When you sign up, Tandem will review your application to make sure their platform remains safe and that the person you get matched with is also a keen language learner.