Homebridge is a lightweight NodeJS server you can run on your home network that emulates the iOS HomeKit API. It supports Plugins, which are community-contributed modules that provide a basic bridge from HomeKit to various 3rd-party APIs provided by manufacturers of "smart home" devices.
I set this up last night and it took about 30 minutes to get the Homebridge service running on my Mac mini and link it to my WeMo plug (the only smart device I own that doesn't work with Siri). This feels "tacky" but it does seem to work so far. I am very happy to have a fully HomeKit-capable house.