Rhasspy is a opensource voice assistant meant to be used with home-automation software such as home-asisstant.
I packaged so far most component to make it usable for nix. Right now one can install it via NUR
nix-shell -p nur.repos.mic92.rhasspy --run 'rhasspy -p en'
There is no nixos module yet, but I have a small snippet that allows to start rhasspy as a systemd service in my configuration: https://github.com/Mic92/dotfiles/blob/2e88e79cfb7b90e800a9590f7bf443b81300f0d0/nixos/turingmachine/configuration.nix#L232
Note that not all component are packaged yet, so have a look at https://github.com/Mic92/nur-packages/blob/e871c0592da15535f5831e4a713d7dc38f7ee0e4/pkgs/rhasspy/default.nix to see what components are available.
I plan to upstream rhasspy and its depedencies to nixpkgs based on popular demand.