Great episode. Nice to hear a few of the ones I've used and known about mentioned as well as some others I've not known about. One that wasn't mentioned that I recently came to discover is called Mojeek. More information about Mojeek below.

Mojeek: https://www.mojeek.com/

Wikipedia entry on Mojeek: https://en.wikipedia.org/wiki/Mojeek

SDF, the well-known public access UNIX system since 1987, has its own Whoogle instance: https://whoogle.sdf.org/