Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Webhook.site - Instantly generate a free, unique URL and email address to test, inspect, and automate (with a visual workflow editor and scripts) incoming HTTP requests and emails.
ioBroker - flexible and modular application for the IoT and Smarthome
Hookdeck - Hookdeck makes it simple to build and deploy reliable, testable, and debuggable applications that rely on webhooks.
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
Svix - The enterprise ready webhooks service, open-source and in the cloud.