slash pages
Fun little guide to all sorts of "common" pages you could add to a website. I imagine most people would never discover them, but I like it as an idea.
giscus
A widget for blogs and similar that uses GitHub discussions as a comments section. Might be a good idea for my own blog.
Indexing outgoing blog links
Nice idea that I might have to try myself some time: index and analyse the outgoing links from blog posts to see what it is you link to the most.