The main difference - You can maintain knowledge hierarchy for topics, which differentiate it from Medium. Second, is collecting the bits and pieces for topics i.e. videos code snippets and sub topics. In Other words, Topics are root level topic for anything(Initially we are targeting only programmers), under a topic you can create sub topics i.e. video, note, code snippet, how to, best practice to explain a topic better. You can also create sub topics under topics to maintain the knowledge hierarchy.