No, there isn't a plug and play one yet, but I've have great success with Home Assistant and the Home Assistant Voice Preview edition and its goal is pretty much to get rid of Alexa.
I'd imagine you'd have a bunch of cheap ones in the house that are all WiFi + Mic + Speakers, streaming back to your actual voice processing box (which would cost a wee bit more, but also have local access to all the data it needs).
You can see quite quickly that this becomes just another program running on a host, so if you use a slightly beefier machine and chuck a WiFi card in as well you've got your WiFi extenders.
I'd imagine you'd have a bunch of cheap ones in the house that are all WiFi + Mic + Speakers, streaming back to your actual voice processing box (which would cost a wee bit more, but also have local access to all the data it needs).
You can see quite quickly that this becomes just another program running on a host, so if you use a slightly beefier machine and chuck a WiFi card in as well you've got your WiFi extenders.