Smart Speaker using ReSpeaker 4-mic array

Some time back (few years), I bought a ReSpeaker 4-mic array for mt RPi3 to build a “Google” kind of smart speaker I heard about in Hackspace magazine.
It actually worked! But it required an account with Google and it was eventually a cost item.
Does anyone know of any similiar projects I could take on that DO NOT require an account or an internet connection? (i.e. all processing is to occur on my network)
In other words, I wish to construct a Google or Amazon kind of smart speaker where everything is on my own in-house network!
I have just finished constructing a smart speaker kind of device using my Amazon Echo Dot without any ongoing cost. It does require an Amazon account because the speech recognition is done on the Amazon servers. However, there is no recurring cost associated with my use of the Echo Dot to control lamps and switches in my home.