When launching your online courses, what feature do you consider a must?

That's a good question. I suppose if we looked at all market segments, verticals, and geographies that the most common denominator would be to have an Authoring tool (even if a basic markdown editor), a system of record (to keep track of courses, lessons, users, etc), and a basic invite/registration flow. Nice to have features for the market in general may be must haves for certain markets. For example, if the company is focused on Enterprise sales, the product may need to support SSO with SAML and the like, whereas a solution that focuses on selling to Instructors (individuals and training agencies) may need a set of features that helps them monetize their knowledge. To be honest the must have feature(s) for any solution to host courses successfully would have to have a seamless, easy-to-onboard, and well documented user interface. If that doesn't exist then nothing works ;-).