You can add an HDR-style effect to the image, whereby the darker areas appear brighter and the bright areas appear darker - giving your image more dynamic range. This gives you an image which looks more akin to how the human eye sees it, rather than a camera.
Image sharpening tools emphasize the edges within an image. This can be applied to a blurred image to make it appear sharper and more detailed.
You can apply a mirror effect to the image, allowing you to experiment with creating symmetrical images.
You can add captions and titles to your photos.
Using the brush tool you can paint across the image, or use it to make small adjustments to touch up the image.
You can build up an image using layers, adjusting the settings for each one independently. This is a sign of a more powerful image-editing app, and allows you to create more complex images.