I am in the process of trying to migrate from Gnome to KDE but one thing that is stopping me making the transition is the lack of a reading strip applet. Gnome has this excellent extension that provides the user with a customisable and easy to use reading strip (the extension is literally called Reading Strip).
The extension lets you guide a transparent coloured line over whatever you are reading to make it easier to focus and maintain your place. It also has a focus mode that darkens everything outside of the reading strip. As someone with Dyslexia, this has made a big difference to my workflow, especially when reading dense documents and papers. In fact, it was a bit of a eureka moment when I first discovered the extension, much more useful than the transparent coloured plastic pages that get recommended to those with reading difficulties.
Here is an example of how I use the reading strip with the optional focus mode:
It is a shame there is no equivalent on KDE as it makes reading a lot harder without. It would be great to see KDE Plasma integrate a similar feature within the desktop. Even just as an applet/plasmoid we could pin to the top/bottom panel. It being officially integrated into the desktop would also be a positive as there would be less risk of it breaking or being abandoned as in the case of a single Gnome extension.