ioBroker - flexible and modular application for the IoT and Smarthome
Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
SEQUEmatic - SEQUEmatic lets you build sequences to link together your various smart devices.
Nim Home Assistant (NimHA) - Nim Home Assistant is an open-source home automation platform running on Nim.
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
MisterHouse - MisterHouse is an open source home automation program.