Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Intel NUC boards - Four-by-four inch Intel NUC boards come with a soldered-on processor.
ioBroker - flexible and modular application for the IoT and Smarthome
esp32 - A very cheap small chip, compatible with Arduino.
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
ESPRESSObin - Electronics, Single Board Computer, and x86