The idea of bookmarklets is so simple that I suspect many people use them without realizing it. A bookmarklet is basically just a specially-crafted bookmark for your browser which performs special tasks. This can mean performing custom actions on the current page or generally improving your web browsing experience.
Technically, bookmarklets are short snippets of Javascript code which can do just about anything. They’ve been around for a long time, but I’ve only been using them a few years. With the increasing prevalence of cloud products and services, I expect their usage will only increase. Bookmarklets make it easier for you to do everything you need to with just a web browser. As such, I’m keeping a list of the most useful.