Headers.me - Create social cover images that get you followers
Photopea - Online photo editor, which can work with PSD, XCF and Sketch files (Photoshop, Gimp and Sketch App).
Figen - Free post cover & background generator tool
Replace Cover - Create beautiful cover art for your Spotify playlists
Blog Cover - Cover image generator for your blog post
Featured Image Creator - Stunning social sharing images for blog posts in seconds