AC3ME. Probably the most useless ham licensee ever. Wanted to be able to say hi on a local repeater for fun and testing a handheld I got, turns out it's not too hard to get US amateur extra when you already know most of the electronics theory and just need to memorize some rules and adapt to terminology, but I don't really use it very actively. But glad I have it - I have some beacon design projects in mind for the someday maybe pile, but basically everything I play with is in the ISM bands and I usually work a layer or three above physical.