MXI is the Maxwell Image format, that will be full operative in a few months.
MXI is a high range dynamic format, that don't operates in rgb space, but in device independent one, like xyz, xyzlab, etc. and if you desired it can support spectral space. ( the energy that arrives to film for a set of wavelengths of light ), useful for more scientific applications.
Other features: MXI allows to change tone mapping parameters without having to re-rendering, as for example gamma correction. Allow yo to replace comments in your image, to protect your comments or image with password so that no one could modify your MXI, etc. And probably will allow you to re-render the image form the last point the render of this image stopped.
There would be a MXI viewer/editor to support MXI images.
Maxwell will support MXI as textures. In fact, when a object has a MXI texture, it will emmit light according through the MXI spectral energies. Is something like HDR, but applied to the object.