In PL/SQL Developer when you select something and press execute, then will execute only selected query.
It is really helpful feature.

I have added this to the list of enhancement requests.

I notice there are 2 execute buttons now, 1 executes the current only and the other all in the window. I interchanged the shortcuts for this as I usually only want to execute the current statement and F8 is easier and is my shortcut in PL/SQL Developer as well.