By and far the smallest I have every seen is the Stuttgart AirFrance lounge. It is about the size of a living room, with maybe 20 chairs max. Decent selection of stuff but it sure is tiny
. That's the whole thing, although I think that may have been a temporary lounge for a few years, haven't been back through it in over a year, but it was there for at least 4+ years as I was traveling through. Literally the only beer available was a bottled german pinecone beer.. and I didn't have somewhere to sit multiple times.