Organized into categories like Apps & App Store, HomeKit, Notifications, Conversion, Messaging, Calendar, Translation, and more. Each section, which can be scrolled through on a single page, includes a range of different Siri commands relevant to each category.
When using Siri, Apple includes a list of sample commands in a "Some things you can ask me" popup, but it only scrolls through a handful of messages and isn't as comprehensive or useful as the Hey-Siri.io website. Hundreds of commands are included on the site, including some of Siri's more humorous responses to questions like "Knock, Knock" or "Why did the chicken cross the road?"
While Siri is only available on iOS devices at the current time, starting this fall, Siri will also be available on Macs through macOS Sierra. Hey-Siri.io includes both iOS and Mac commands, and switching between them can be done using the Settings button on the site.