Many people are familiar with presentation software such as PowerPoint, Keynote, Google Slides, or Prezi.
There are also tools that use HTML and CSS to create engaging presentations.
reveal.js is "an open source HTML presentation framework. It's a tool that enables anyone with a web browser to create fully-featured and beautiful presentations for free."
The people behind reveal.js also have a commercial service, Slides.com, which provides a nice authoring, hosting, and sharing platform for reveal.js presentations.
remark.js is a little less fancy than reveal.js, but presentations are natively authored in Markdown. (Slides.com has Markdown presentation import in beta as of this writing, 2023-06.)
impress.js creates panning, zooming, and rotating presentations, similar to Prezi. Hovercraft! is a software tool that assists in creating and especially editing impress.js presentations. Crucially, Hovercraft! enables relative positioning (and other methods) of slides in space, which allows easier insertion and deletion of slides.
S5: A Simple Standards-Based Slide Show System is an early (2004) HTML/CSS presentation tool that I (Pete) used back in the day. It was (and still is) clean and straightforward to use.