The RevealJS presentation module is an alternative to PowerPoint, PDF, and other
web-unfriendly formats.

It uses the free and open source JavaScript slide show library, reveal.js

See: https://github.com/hakimel/reveal.js which includes helpful documentation
for creating and editing presentations.

reveal.js can also be used as a standalone presentation player (in a web
browser) and be used for creating, editing, and previewing presentations before
uploading them to Moodle.

There is an online presentation editor at: http://slid.es However, it is not
free and open source and creating a "freemium" account is required to use it.