The best alternatives to Coaster are Unsplash, Background, and Irvue. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Coaster?
AssemblyAI— Speech-to-Text API with superhuman accuracy
Irvue brings thousands of stunning high-resolution photos from Unsplash to your desktop. Enjoy new artistic wallpapers everyday with this small application, which lives in your menu bar.
DailyWall for Mac is an app that will change your wallpaper to one of the beautiful photos from a curated collection gathered across Unsplash, Pixabay and Pexels every day at 10AM.