Espressif started out, way back, as a consultancy company to develop specialized silicon for customers, before building generally available WiFi chips. I imagine those are those chips. Not sure where you get those part numbers, though; I don't see them on that site and the ESP3000 seems to be made ...

Hi. I was on the Wayback Machine (espressif.com, 2011) and I found ESP6000, AS5900 and ESP3000 chip series on the products section. Can anyone clarify these chips?
https://web.archive.org/web/20110201132 ... om/#expand