What the heck is that thing?

Viridian is right, it's a small round glass topped table.

Viridian is right, it's the spaceship Michael Fremer flew in on. : )

Given its size and location, I assumed it is the seat of the chair/stool for the piano player.

Speaking of Mikey, has anybody actually heard his comedy LP? I haven't, but I did hear a short piece on a local Boston compilation album from the 70's I found at a used record store, called "30 Seconds With Michael Fremer". He impersonated a ditzy Long Island (or maybe Brookline?) princess doing her nails while gossiping on the phone to her girlfriend Rita. I considered buying it and using it to blackmail him... ;^)