Photopea - Online photo editor, which can work with PSD, XCF and Sketch files (Photoshop, Gimp and Sketch App).
THE PABLO DOT LIFE - The Life of Pablo artwork generator™
Replace Cover - Create beautiful cover art for your Spotify playlists
Coverify - Create your own custom cover art for Spotify playlists.
Headers.me - Create social cover images that get you followers
Podcast Cover Art - Discover the world’s best podcast cover art