Overlays! is a Mac application that comes in handy when reading news articles, ebooks or any other type of text document on your computer. This program displays a colorful bar on your desktop which you can control with your mouse and which helps you follow a line from the text you're reading.
The utility lives on your Menu Bar from where you can enable or disable the overlay bar and configure the program's settings according to your needs. You can choose a color for the overlay bar, adjust its opacity level and height, and select its proper distance from your mouse cursor.
In my testing, the application worked flawlessly, without slowing down the performance of my computer. I also like that the Preferences menu stays on top of all windows.
The one thing I'd add is an option to define a global hotkey for immediately enabling or disabling the overlay bar. This way, I wouldn't need to go to Menu Bar to complete the aforementioned tasks.
In conclusion, I think, you should try this program if you're looking for an easy way to follow lines when reading text on your Mac. The application is very simple to use and configure and is free of charge.