It edits pixels
http://www.danielx.net/pixel-editor/
Limited color palette (4, 8, 16, 32, 64, 128, or 256)
Pencil
Brush
Eraser
Eye Dropper
Paint Bucket
Ellipse
Solid Rectangle
Rectangle Outline
Line
Normal Flip horizontally Flip vertically Quad
0-9 Select nth tool
Fork on Github https://github.com/STRd6/pixel-editor/fork
Go to http://danielx.net/editor
Load your fork by clicking "Load Repo" and typing in "/pixel-editor"
When it loads click "Run" to make sure it works
Click "New Feature" to start working on a feature branch
Modify the code and click "Run" to see your changes.
Click "Save" to push the code to your feature branch
Review your branch on Github to make a pull request.
Hopefully that works, but if not open an issue at https://github.com/STRd6/editor/issues/ and let me know what's not working.