With a very suggestive name, ImageCrop does exactly that: It lets you crop images in many different ways. The tool is very easy to use, which is good, but I could not find any useful help documentation whatsoever.
The application’s interface is extremely simple. It lets you preview both the source image and the result after processing. There is also a dropdown list from which you can pick the desired crop mode. In this respect, you can crop the image from the center, top/left or bottom/right. Likewise, you can use the Scale-to-fit option.
To be honest, the list of things this app cannot do is much longer than that of its abilities. So, I will mention only those I find most annoying. In this respect, there is no way to freely crop the image, just like you do with many other similar tools, by drawing a rectangle enclosing the part of the image you want to keep. Likewise, it was not possible to set the desired output dimensions.
All in all, ImageCrop does not have much value as a standalone application since it is actually intended to serve as source code you can reuse with NSImage. The app is opensource and a compiled demo version is available from the developer’s site.