Screen ruler with simple color picker and screenshot tool. Measures a selected area. Has the magnifier for precise selection.
Overlaps the screen with a transparent window for drawing. The taskbar does not overlap.
Selecting an area with Ctrl key leaves the selection when the mouse button is released. This used for area screenshot.
You can draw on the screen before make screenshot. Use mouse with Shift key. Tools in the screen context menu.
There is also mode for resize and moving capture area.

Hotkeys:
Ctrl-Space, Mouse middle button - Capture current color
Ctrl-C - Capture current color and copy to clipboard
Ctrl-S - Copy screenshot to clipboard
Ctrl-Z - Undo drawn object

0.4.2 - 10 sec delay for screenshot when Alt key pressed. Solid line always for area < 12 px.
0.5.7 - Desktop overlap indicator. Areas menu item.
0.7.4 - Resize area mode

If you cannot draw an area in Manjaro set gtk2/fusion style in Qt5 Settings.

You can extract contents of an AppImage and use one program file if your system has libraries.
./mdruler-074-x86_64.AppImage --appimage-extract
Files will be extracted to "squashfs-root" directory.
The bundle includes files install.sh and uninstall.sh for installing the bin-version.
You can check files for viruses on virustotal.com.