r/WhatIsThisThing, r/TipOfMyTongue, and similar subreddits. Some of the simplest and best examples of the power of crowdsourced knowledge. Take a simple question with a simple answer that is basically impossible to search through conventional means, but through the power of those communities you can get your answer in minutes. Simply amazing.

Lemmy is going to have to get huge before it can really replace them. :/