nip2 is a GUI for the VIPS scientific image processing library. It's a little like a spreadsheet: you create a set of formula connecting your images together, and on a change nip2 recalculates.
It can load images in most commonly used formats, but also in scientific formats such as Matlab, FITS, OpenSlide, OpenEXR, and others. nip2 is especially useful with very large images. You can easily work with multi-gigabyte images even on a modest computer.