Quix. Quix is a bookmarklet which opens a prompt, and then responds to commands.
When you type whois, for instance, it’ll take you to a page with the whois of the domain you’re currently on. It can also understand more complex commands, like gs help, that will make it go to Google, searching the current site for the text “help”. You can also select a word, and use that as extra input for the command. So for instance, when you select the word dictionary, then open Quix and just type d in the prompt, it’ll take you to a Google define: search for the word dictionary. The same would happen if you had not selected anything and typed d dictionary directly.