openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
FHEM - FHEM (TM) is a GPL'd perl server for house automation.
Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Conrad Connect - Service for managing smart home devices
IP-Symcon - IP-Symcon is the innovative centre of your entire building automation!
Homebridge.io - Homebridge is a lightweight NodeJS server you can run on your network that emulates the iOS HomeKit...