Ask HN: Best online course platform

I am helping a friend who runs a mindfulness / therapy business to set up a new online business. The business will provide courses (video and some interactive quizzes) to subscribers for a flat fee every month. Majority of the content will be videos. I am looking for a good, secure (hopefully open source solution) with responsive design (mobile access), card payments support, enrolment, and simple course setup with certificate upon completion. Any takers? I had a look at Open EdX, which looks comprehensive but also very complex (Ubuntu 12 as only platform, really?), Moodle (which is too focused on unis), and Lifter (which is too limited and runs on Wordpress, which I don't trust). Any ideas / suggestions for a platform?