PyWeek - Undocumented Feature
The title isn't a euphemism, this is actually an undocumented feature:Right clicking will leave the current building mode if you are in one and will cancel tasks if you aren't.
Two people independently complained about the lack of such a feature and I realised that it should have been somewhere in the instructions.
— Chard on 2007/09/11 13:46 of Super Effective 5
Comments: (log in to comment)

By gcewing on 2007/09/12 00:29:
Is there an alternative for those of us with button-challenged mice?By Martin on 2007/09/12 08:22:
gcewing: Option-click should work, assuming you're on a Mac. If you're using a one-button mouse on Windows or Linux, I'm afraid you have bigger problems than being unable to cancel tasks.