I've been trying to identify this piece of glassware for ages now. I've been combing the internet and can't seem find anything similar. It looks like some kind of adapter/collecter/trap that sits on the pot and the condenser goes on top.
This glassware is used to separate /remove the light phase from a biphasic (immiscible) liquid mixture. This can be used primarily to enhance liquid-liquid extraction from the light phase to the denser phase. As a mixed distillate collects, the denser phase will eventually siphon back through the side-arm to the flask below and the light phase remains in the collector.