Mac OS 9 really had a 'personal' feel to it and part of that was thanks to Kaleidoscope. Many authors also designed accompanying icon sets, to complete the look.

Japanese authors were responsible for my favorite schemes/icon sets.

Same developer would go on to make Konfabulator for Mac OS X, a desktop widgets application which Apple directly aped for their Dashboard widgets and Yahoo eventually acquired.

The era of Kaleidoscope was so full of creativity, I have a lot of nostalgia for it. My sister and I would have wars for what scheme would be set on the family Performa, and it would change out weekly.

There's also a Mastodon bot that randomly toots out schemes/themes https://social.erambert.me/@macthemes

Idea (I lack the skills to implement):

Train an upscaler/style transfer model on these lovely things (plus Winamp skins etc) to create a teachable AI theme engine.

The about, https://kaleidoscope.hryjksn.com/about