Although I have a lot of bicycle tools, every once in awhile I need something I don't have. Like Neal, sometimes you just gotta get creative. I wanted to disassemble the attachment bolt for a SunTour Cyclone 1st generation rear derailleur, which is nutted on the backside to a short shoulder bolt so you don't lose the nut, but it can still turn. A strip of stainless steel, grinder, and file later I had a custom tool to remove it.
Item 4 in this excellent exploded drawing.