Smoke advertises that it "brings parts of Steam" to the Apple Watch. The hardware is obviously pretty limited, so don't expect to be purchasing or launching games from your wrist. You will be able to view your games and achievements, view store information and see if your friends are online and what they've been playing though.
Perhaps the most useful feature is the ability to view Steam news articles, which can alert you about sales and updates for your favorite games. You can also tap a news article to save it to your phone, but this feature is only available to paid users.
The Smoke app page notes that for most of the features to work, your Steam profile needs to be set to public. If that's ok with you, you can download Smoke for Steam for free from the App Store.