Homegear!

openHAB is a Java-based open-source home automation platform that integrates and combines a vast range of different smart home systems and technologies into one single solution.On top of the unified abstraction layer all connected devices are available for the overarching automation rule engines and different user interfaces.

FHEM (TM) is a GPL'd perl server for house automation. It is used to automate some common tasks in the household like switching lamps / shutters / heating / etc. and to log events like temperature / humidity / power consumption.

homebridge - HomeKit support for the impatient

IP-Symcon is the innovative centre of your entire building automation!