Here is a free Adobe AIR based application, named as Xe-IMG Image Editor. Apart from being machine independent (as it is an AIR based application you can run it on any platform) it has very easy to use interface, and can also be used as format converter, i.e. you can change an image to other file formats like png, jpg, bmp, and PDF as well.
There are no heavy settings like options, it has a minimalistic interface, and so are the available options, have a look.
You can add Black & White, Blur, and Embossing like effects in just one click. It also supports using an online image to edit it, you can enter the link for image directly in the right panel, and load it to edit. The rotation, and zoom features can be used by sliding the controls on top, but they aren’t of any use, apart from just to view the image by rotating it around the vertical axis, and to have enlarged view.
Though with few options, but still Xe-IMG Image Editor is a great piece of software. If you want a simple image editor, this is for you.
If you love AIR application you can browse through other Adobe AIR based applications.