GIMP
FreeA free, professional image editor — the open-source answer to Photoshop
Open Source No Ads No Tracking Offline No Sign-up Cross-platform
A full-featured raster editor with layers, masks, channels, filters and scripting. Install once, never subscribe.
Why we picked it
As Photoshop moved to monthly subscriptions, GIMP remained the "download once, use forever" option. Layers, masks, paths, batch processing — the essentials of serious photo work are all here, plus a rich community of plugins and brushes.
Its interface differs from PS and takes some adjusting, but for the vast majority of editing and design work it's more than capable — and completely free and open.