Watchify is a Spotify client for the Apple Watch built using the Spotify iOS SDK. A Spotify premium account is required to use Watchify.

Watchify allows you to chose from your Spotify songs and playlists and play them from your iPhone. This is ideal if you're wearing headphones that are already connected to your iPhone.
Watchify allows you to pause, play, skip, and replay songs just like the official Spotify app directly from your Apple Watch.