More than 300 different modules(adapters) that can be interconnected with each other. E.g. Homematic or KNX can control HUE or sonos and vice versa.
Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
Domoticz - Domoticz is a lightweight Home Automation System
Google Home - Set up, manage, and control your Chromecast, Chromecast Audio and Google Home devices.
Jeedom - Jeedom is a complete home-automation software.
Home - Securely control all your HomeKit accessories from your favorite iOS device.