FlexRuler 2.3 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. FlexRuler for Mac relates to Design & Photo Tools. 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. This Mac app is an intellectual property of dropframe.jp.
From the developer:
FlexRuler is a simple desktop ruler application, which allows you to customize your ruler color and transparency. The program can also enlarge pixel views with the Loupe window. Rulers can be shaped into any rectangle anywhere on the screen. Each can have its own color and even rulers of the same color can have different transparency.
You may want to check out more software for Mac, such as Smith Chart for Mac, Digital Studio v5 or Piranesi, which might be related to FlexRuler.