This looks like it's going in the same direction as Deckset (https://www.deckset.com/) and reveal-md (https://github.com/webpro/reveal-md) – neat. I love the former (just works really well for me) and would really want to like the latter (open source! no license needed, collaboration-friendly, customizable), but it makes me fight my tools just a bit to much. Part of which is intentional, of course – the point of these tools (for me) is to not get sucked into a handcrafted slides rabbit hole, because they resist me very strongly if I try, but things like autoscaling lots of text on a single slide just have to work (couldn't find a decent-looking way to do this in reveal-md without magic – works nicely in Deckset).

Yours looks like it could fill that gap (featureful yet easy to use), though (on first glance, I'll admit) it still appears to be kinda limited. I can't figure out how to exit presentation mode, I'd prefer to have somewhat more explicit slide boundaries (e.g. using the Markdown "---" separator), so I can have multi-line slides with paragraphs, plus I could throw my Deckset markdown slides at it and have them work with relatively minor changes. I think the mix of Markdown and HTML in the examples are a bit confusing, maybe it would be better to stick to just Markdown?

I couldn't figure out how to have an image and text side-by-side (I like to do this in Deckset to have e.g. a vertical process diagram on the left and the most important remarks/caveats on the right). Other things I personally am missing are multi-line code snippets, text on top of an image background (ideally desaturating/blurring the image for readability, Deckset does that well), and speaker tools.

What's there is really lovely, though. I love how super snappy it is, the themes look pretty good, very nice and minimal. It's mostly very straightforward to use and already has a bit of polish, which is neat at what looks like a pretty early stage. I think this looks really good and promising!