I have come across Exerb, which produces a Windows executable from your Ruby program with an interpreter included, so it won't even require Ruby installed to be executed in Windows. Moreover, you can make the binaries in any platform with Ruby.
That's yet another great thing for Halk, because authors will be able to distribute presentations for Windows as a stand-alone .exe file with no further requirements (unless the presentation itself have dependencies. For instance, a Python course would normally require Python installed to let the reader run the code snippets of the slides). I don't know the size of the executable, but at least you have the choice to provide one.
I don't particularly like transition effects, but it would be a fancy feature, so I rapidly thought I could provide them out of the box so authors could use them if they wanted to just setting a parameter in the corresponding slide. They worked in Mozilla (Windows and Linux) and Explorer. They didn't in Konqueror (which cooled my enthusiasm down a bit), and don't know what happens with Galeon or Safari (if anyone tries please let me know, I would appreciate it very much to take a decision). So I don't know what to do. It might be reasonable to provide them with a warning (the slides themselves would be seen alright in Konqueror anyway, so having the transition won't hurt in that particular browser).
Talking about browsers, another cool thing about all this is that with a non-fancy theme (which I'll certainly provide with the distribution) one will be able to give the presentations in some text-based web browser. I saw a couple of presentations running on terminals in the YAPC::Europe and they were way cool. BTW, the engine of one of them, which was about Parrot's performance, was written in Parrot bytecode, how devil.
I am not coding this week to let the ideas rest a bit.