The Gateway Emporium was a shop owned by the Master, or the Manager, at the end of a parallel universe. It sold many different items, from sonic devices to lottery tickets. They took credits as currency, as well as memories.
It supposedly contained a portal to another universe, but this led nowhere. Those "saved" by the Manager were atomised by the portal, and used as a potential energy power source for the Master's own escape. (AUDIO: The Emporium At The End)