My radio hobby concerns all kinds of activities, from amateur TV, to ISS contacts, mounbouncing as well as FOX hunts.
Since I started with CW a few years ago, my favorite QRP rigs are my mint-boxed 'PIXIE3' rigs. Tuneable, about 500mW and with 55 components about as minimal as you can get.
Contacts with the most reduced power have been in my pirate time in the 80's, where I was experimenting with big antennas and transmitters with huge dynamic range. Powers as low as 10 nanoWatts have been used to make QSO's. That really was QRP, even in wideband FM.
73,
Alex