Homebridge allows you to integrate with smart home devices that do not support the HomeKit protocol. Here are just some of the manufacturers you can integrate with.
Integrations are built by the community, and tagged as homebridge-plugin on NPM.
Homebridge is powered by Node.js and can run on any computer. Even a $5 Raspberry Pi Zero.
After installing Homebridge, it remains running and connected to your network, ready to service requests from Siri.