High-quality image scaling
If your graphics hardware is fast enough, Xee can use it do very high-quality image resizing, both when scaling up and down. Make sure that the "Scaling Quality" menu is set to "Medium" or "High" to enable this functionality. For the technically inclined, Xee uses a gamma-compensated Bessel filter.
If you enable the option "Show pixels when zooming in", Xee will also apply special filtering to show as sharp pixels as possible, even at fractional zoom levels.
Xee uses the Image::ExifTool library to extract metadata from image files. This is one of the most extensive and capable metadata libraries available, and it will supply you with a plethora of information about your images.
JPEG creator identification
JPEG files use a data structure called a "quantization table" to define the level of compression. As there is a lot of freedom for a program to choose these tables, and digital cameras especially use a large number of different ones, having a big list of known quantization tables can give you an indication of what program or camera created a given JPEG file. This can give you a hint about whether an image has been manipulated or not.
Xee contains an extensive database of tables, and will present you a list of possible creators that it knows of.
(Note that this information will never be perfectly accurate, and should not be relied on to be correct.)
Xee uses a multi-process model for loading images. This is similar to how web browsers like Google Chrome work, and prevents bugs in the image loading code or corrupted images from crashing the entire image viewer. It also offers better resistance against maliciously created images.