Subtle Patterns Bookmarklet
A bookmarklet that previews background patterns from Subtle Patterns on any live website. It reached the Hacker News front page in 2013 with 347 points.
Choosing a background pattern meant downloading it and trying it in your stylesheet. The bookmarklet let you browse the Subtle Patterns collection with the arrow keys and see each pattern in place on the site you were working on. A Chrome extension version followed.
The original page is still online.