Blender 2.8 stuck on some selection mode - no idea what it is I'm in object mode, there's a circle around the cursor - exactly like what would be there if circle select were active, but it's not active.
Single click on things does nothing, I need to double-click to select anything.
And hitting C simply enables the normal circle select.
I have no idea how to turn it off.
BTW - it only applies to this project, none other. So I think I just hit some key by mistake - Thanks.
Tap the 'W' key.

I'm suffering this problem right now. I was using 2.82 while following a tutorial based on 2.78, and heard "tap W" to get a menu to pop up for doing something.  Nope, not in 2.8 and later. These days, 'W' turns on this permanent circle select mode.