I love browsing https://www.themarginalian.org whenever I have a few hours to kill. It's a bit like TVTropes, but much more "literary" for lack of a better word.

The author has spent decades building a digital commonplace book of everything she's ever read, and hyperlinked everything together in a way that you can get lost in her notes for hours on end and never surface. It's one of my favorite websites on the internet, and the best example of the power of marginalia and hypertext.