The best open source alternative to Google Home is Home-Assistant.io, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Google Home and 19 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Google Home are openHAB (Free, Open Source), ioBroker (Free, Open Source), MediaPortal (Free, Open Source) and Domoticz (Free, Open Source).
Oblecto is a media server, similar to Plex, Emby, Netflix and others. It runs in the background on a home server to index your media such as movies and TV shows to make them searchable and streamable through a REST based interface.
Homify is an open-source smart-home platform running on PHP using the Laravel framework. The entire application is built using a modular approach so support for other devices or actions can be implemented easily.
Domogik is a free (GPLv3) Home Automation solution. It allows you to: Controlling your lights, shutters, etc. Monitor your home (temperature, electricity, ...). Create scenarios to make your home more independently. Controlling your home with Voice.
EVA ICS is a platform for automated control and monitoring systems development, for any needs, from home/office to industrial setups. It is completely free for non-commercial use as well as for commercial, on condition that enterprise integrates it on its own.