Are there similar retro-UI systems for other older interfaces? While I don't have that much nostalgia for Win98 myself, I could see how it could be cute to have similar systems for classic (System 6-7) Mac, Amiga, etc. I've seen websites that try to go for these looks, but I think they were manually done.
What would be nice is if there was something like a standard test or demo set of HTML for all these to work against, which would enable a way to switch themes.