I still think your promoting the view of “this is obvious to me so it should be obvious to everyone”. Even your explanation would be confusing for someone who’s not an IT guy - what does it mean “end my user session?” People rarely go to the start menu to deal with their computers’ “on-ness”, they just press the hardware button that has an incomplete circle with a line on top or often no marking or label at all. Or they close the lid and that makes them think of their laptop as “off”.
If you travel a lot, Toilet finder.
Edit: and not an app, but a website: Pairdrop - really useful for cross-platform file sharing, especially when you just need to email to colleagues something you snapped with your personal phone, but yoe have overly tight IT systems in place at work that stop you from connecting your personal phone to your email or OneDrive.