Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Jovo - 🗣 Build cross-platform apps for Alexa and Google Home
ioBroker - flexible and modular application for the IoT and Smarthome
API to bot - Convert your API to Alexa skill or Google Home app in 5 mins
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
Alexa for Business - Using Amazon Alexa’s voice enabled devices for workplaces