The AIY Voice Kit from Google lets you build your own natural language processor and connect it to the Google Assistant or Cloud Speech-to-Text service, allowing you to ask questions and issue voice commands to your programs. All of this fits in a handy little cardboard cube, powered by a Raspberry Pi.
Everything* you need is provided in the kit, including the Raspberry Pi.
* Additional items needed - Android Phone able to download AIY Projects App and 5V USB phone charger able to provide 2A current
* You need to be able to use SSH and have a Google Cloud Account (free-tier available) for the Voice Kit to work.