I just published a new article, Quick Tip: Using The Screen Utility To View Arduino Serial Output, on how to use the screen command line utility to view the serial output from an Arduino development board. This can be quite helpful if you are using the arduino-cli command line utility for your sketches.
Thanks @woolsey. Regarding this:
By the way, if you are on a Windows system, I understand a terminal program, such as Putty, should provide similar functionality to the screen utility.
I did an investigation about this earlier this week and the best option I found for a Windows command line terminal is the Plink tool included with PuTTY.
@woolsey: Can I suggest that you state what platform is required to run the "screen" app?
I've used putty and not found it very helpful. Because the com port the arduino IDE can not upload while its connected.
Termite is a FREE portable (no install) serial monitor that runs well under windows.
It has an option to keep the window on top; so you can leave it floating over a free area of the IDE.
Also an easy way to disconnect when you want to upload, and reconnect after uploading.
(you just click in the box top left)
My understanding is that the screen command line utility is available on macOS and most Linux based systems.