Looks really cool, congrats. By the way, I love your hakim.se experiments lab. Such a treasure trove of cool ideas. Really, really inspirational. Best of luck with Slides!

Can you share a slide within a blog post without using an iFrame

Nope, presentations can only be embedded as iframes.

Beautiful editor, what's it built with?

Most of it is custom built rather than using a larger JS framework. We do use a whole lot of libraries for specific tasks though, like moment.js for date formatting, Ace for code editing, Spectrum for the color picker.