Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Astra by Cesbo - Talk to Alexa anywhere, from your iPhone
ioBroker - flexible and modular application for the IoT and Smarthome
Reverb - Use Alexa on your Mac, iPhone and Android
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
Amazon Blueprints - Create your own Alexa Skill in minutes