As of my last knowledge update in January 2022, here are five popular photo editing apps:


1. Adobe Lightroom: Known for its powerful features and professional- grade editing tools. 


2. Snapseed: A user-friendly app with a wide range of editing options and filters.


3. VSCO: Loved for its stylish filters and minimalist interface, it's a favorite among mobile photographers..


4. Afterlight: Offers a variety of filters, textures, and frames, with an easy-to- use interface.


5. Prisma: Known for its unique art- inspired filters that transform photos into artwork.


Keep in mind that app popularity can change, and new apps may have emerged since my last update. Always check for the latest reviews and features when choosing a photo editing app.