InPixio Photo Editor is a free image editor, extremely basic but with app-like 1-click ease of use.
Open a picture and you can apply a small selection of filters with a click: "Artistic", "Black & White", "Colour", "Monochromatic", "Vintage", a few more.
There's no fine control here, but click the Adjustments panel and you can select a starting shade, tweak hue and saturation to produce more interesting results.
Other Adjustments include sliders for Temperature, Tint, Brightness, Shadows, Highlights, Contrast, Clarity and Saturation. Dragging any of these updates the preview image immediately, or you can opt to view before and after images for an instant comparison.
Our favourite feature is probably the Crop tool. You can drag and drop a freehand rectangle within your image, set the crop area to a predefined ratio (1:1, 2:3, 3:4, 4:5, 5:7, 9:16), a custom ratio of your own, even rotate the image by an arbitrary angle, all while a grid helps you keep everything lined up.
When you're ready, InPixio Photo Editor has 20 frames you can (optionally) apply with a click, before saving the results locally or uploading them to Facebook.
Despite its name, this isn't a "real" photo editor - we couldn't find a way to resize images, or even sharpen them. But it is very easy to use, and the crop tool is excellent, so if you just need something to tidy up an image, add a frame or simple colour filter, then InPixio Photo Editor might be good enough.