Conrad Connect - Service for managing smart home devices
Thingsboard - Thingsboard is an open-source IoT platform for data collection, processing, visualization, and device management.
FHEM - FHEM (TM) is a GPL'd perl server for house automation.
Node-RED - Node-RED is a programming tool for wiring together hardware devices, APIs and online services in new and interesting ways.
Homebridge.io - Homebridge is a lightweight NodeJS server you can run on your network that emulates the iOS HomeKit...
n8n.io - Free and open fair-code licensed node based Workflow Automation Tool. Easily automate tasks across different services.