As others have commented, the open source home assistant project can take voice commands and perform smart home functions like turning lights on and off, reading off the forecast, taking down notes, etc etc. But it does have limits, you will have to script any kind of complex commands, like pulling headlines from an RSS feed, or playing spotify playlists, or really anything that requires fetching info from an API, it won’t do those kinds of things out of the box.

The other factor which others have called out is that it doesn’t currently handle wake word functionality, though that’s been on their road map this year and the Oct update might fix that. That being said, running a dedicated wake word app to fill in that gap is very much possible. See my thread here for more info: https://community.home-assistant.io/t/setting-up-a-100-local-smart-speaker-on-an-android-tablet-using-tasker-and-snowboy-to-handle-wake-word-detection/611435