Chrome: Most of us know about internal Chrome settings pages like "chrome://flags", but it can be hard to remember the names for each of them. Service Pages for Google Chrome saves you from looking them up by storing them in your extensions menu.
Once you install the extension, just click the gearbox icon to call up a dropdown menu of every Chrome service page. The basics like Settings, Experiments, and Extensions are all there, but there are dozens more that you probably never knew existed. For example, chrome://memory-redirect/ shows you how much RAM each of your tabs are using, and chrome://sync-internals/ lets you view and manage fine grained details of Chrome's sync.
Some of the pages are either deprecated or not necessary for your Chrome configuration, so not all of the links will actually work, but you can disable bookmarks that you don't care about in the extension's settings. It might not be an app you use often, but it's great to have when you want to dig through the underbelly of your browser.