GIMP

GIMP is the free image editor people reach for when they will not pay Adobe. Photo retouching, compositing, masks, layers, curves, batch processing through a scripting console, and a plugin ecosystem going back decades. Version 3.2 is current, and it finally brought non-destructive editing, better HiDPI handling, and a GTK3 interface that no longer looks like 2008. GPL-3.0, genuinely free, no account and no tier.

The catch most people hit is not capability, it is muscle memory. GIMP does not copy Photoshop's shortcuts or its single-window habits, so switching costs you a week of fumbling before your hands know where things are. CMYK support is still weak, which rules it out for most print work. Running it is trivial: packages exist for every desktop, plus a Flatpak.

Solo creators and small teams doing web graphics, screenshots, and photo cleanup should stop paying for Photoshop and use this. Anyone doing print production or trading layered PSDs with clients will keep fighting it. For digital painting specifically, KDE/krita is the better tool.

The catch worth knowing before you file a bug: GitHub is a read-only mirror. Development, issues, and merge requests all live on GNOME's GitLab, so the activity signals here understate the project by a wide margin.