Smallest I’ve ever been to (not flown out of) was Pelilu in Palau. It’s basically a gravel strip which is usually a part of the road network (and part of the island tour since in WWII it was important). As far as I can remember an island hopper lands there a couple of times a week.

Strangest “small” one (at least concerning the number of flights) was Ulyanovsk Vostochny (ULY) – the widest and 3rd longest runway in the world, but on the day we were flying out of there on a private jet were the only flight operation during 3 days. They had to activate around 200 people to do everything from clearing part of the runway to doing security checks, escorting us through everywhere. The even handwrote boarding passes so everything could get stamped (for a private jet wit 3 crew and 4 passengers)…