There are several actually.
Photoshop is just "the" standard, like AutoCAD or Office programs.
https://skylum.com/blog/best-free-photoshop-alternatives
For what we do Photoshop is the only choice. That and I have been using it since it was PhotoSytler by Aldus, and they were bought by Adobe, and merged into Photoshop. I remember using it at work on our IBM PC AT 6 MHz computer with a 2 megs of RAM and the huge 32 MB hard drive. I scanned a 8x10 at 300 PPI and then needed to rotate it 90 degrees. I started the rotation at 5:00 when I went home. When I came in at 7:30 is was not yet done and it finished at 8:30. I told the boss we needed more RAM, and another 2 megs for the expansion card was several hundred bucks.
Now I can rotate a file that is a couple of gigabytes in just a few seconds.