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.
Nim Home Assistant (NimHA) - Nim Home Assistant is an open-source home automation platform running on Nim.
My Devices - Drag and drop IoT project builder for Raspberry Pi
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
MisterHouse - MisterHouse is an open source home automation program.