It's not mentioned on the landing page, but Flow integrates with PowerApps [1]. The PowerApps console shows Flows [2], and PowerApps can trigger Flows [3].

[1] https://powerapps.microsoft.com/en-us/

[2] http://i.imgur.com/dKxw9Tz.png

[3] http://i.imgur.com/UjJ7Bcg.png