Open Source Image Editor
An image editor's catch is that its power lives in layers and adjustments saved in a project file, and that file is useless the day a future version or a defunct vendor can't open it - so the format you edit in is the real commitment, not the toolset. The open source editors here keep their working files in documented, readable formats and run entirely on your machine, so a years-old project still opens and your originals never leave your disk.
Excalidraw
Open source virtual whiteboard for hand-drawn style diagrams, wireframes, and collaborative sketches
Penpot
Open-source design platform for teams, with self-hosting and open standards like SVG, CSS, HTML, and JSON
Upscayl
Free and open source AI image upscaler for Linux, macOS, and Windows
ShareX
Free and open source Windows app for screen capture, recording, and file sharing
Graphite
Free open source vector and raster editor with nondestructive layers and a node-based procedural engine
darktable
Photography workflow app and non-destructive raw developer for organizing and editing digital negatives
Krita
Free and open source digital painting app for creating artwork, comics, illustrations, and concept art
PixiEditor
Universal 2D editor for pixel art, painting, vectors, and animation in one app
GIMP
Free and open source image editor for retouching, compositing, and creating graphics