What are some free, open source, or low-cost authoring tools to create e-learning modules?

As mentioned in another post, H5P is a free and open source authoring tool for rich and interactive learning content in HTML5. It’s designed to work on mobile devices as well as on desktop.

You can either add the H5P plugin to your WordPress or Drupal site, or you can create learning content on h5p.org and then embed it your site, just like a YouTube video.

Disclaimer:  I’m a part of the team contributing to H5P.