There is only one file type that uses the .LRLIBRARY extension:
Adobe Lightroom CC Library File
An LRLIBRARY file is an archive created by Adobe Lightroom CC, a digital photo management and editing application. It contains data about a library created by Lightroom CC, which includes the original images and .MCAT catalog file. LRLIBRARY files are the same as the less common LRLIB files.
Adobe Lightroom CC automatically creates an LRLIBRARY file when it is installed on a computer. The file is placed in the "Pictures" folder of your home directory. When you import pictures into Lightroom CC, information about each picture is added to the LRLIBRARY file.
NOTE: Lightroom was formerly known as Photoshop Lightroom.
Updated: January 19, 2018