Developer of Euclid here. I made this app over the last couple weeks mostly to scratch my own itch. As a person who develops a lot of UIs this tool is invaluable to me. Whether I'm working on an iOS app in the Simulator or a web app in the browser, being able to call up fullscreen crosshairs with a hotkey is super helpful to make sure everything lines up. This is also sort of an experiment for me as I've never sold anything on the Mac app store. I would love to know what HN thinks of Euclid, any feedback is much appreciated. Thanks for looking!