It supports rotating, flipping, cropping, adjusting brightness and contrast, as well as adding arrows, circles and text. A major feature is that it checks for the maximum canvas size (which, as I have discovered, conveniently differs between browsers) and resizes the image to fit, so it supports editing larger images as well (an important point, as many users were uploading JPEGs straight from their camera and getting a blank canvas).

You can try it online for free (all processing happens client-side, without any tracking) at: https://photo.kigun.org

Please let me know what you think. Thank you!