There is only one file type that uses the .LRCAT extension:
Adobe Lightroom Catalog File
File used by Adobe Lightroom, a digital photo management and editing application; stores a catalog of information about a collection of images; used for storing organized information about digital photos.
LRCAT files are stored with a supporting data file that has the .LRDATA extension. Both files are saved within a directory that is named using the prefix of the filename. For example, a catalog named "myCatalog" will have files named myCatalog.lrcat and myCatalog Previews.lrdata, and will be saved to a directory named myCatalog.
NOTE: Lightroom was formerly known as Photoshop Lightroom.
Updated: April 7, 2018