Red Lines Tools 1.6 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this free software for Mac is 3bitlab. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. Red Lines Tools for Mac relates to Design & Photo Tools.
From the developer:
Red Lines Tools is a collection of tools created to help developers and designers make beautiful UI. The application allows you to add various elements to the screen, including lines, grid, layout, and various image overlays on top of all windows. All tools have increased accuracy for working with retina screens.
You may want to check out more software for Mac, such as Red Giant Link, Chaikin Power Tools or FLIR Tools, which might be related to Red Lines Tools.