There is only one file type that uses the .LRPLUGIN extension:
Adobe Lightroom Plug-in
Plug-in used by Adobe Lightroom, a professional digital photo editing application; adds new functionality to the software, such as a hook-in to Facebook, Flickr, or another online service for sharing photos; can be created by third-party developers for adding a variety of other software functions.
NOTE: Lightroom was formerly known as Photoshop Lightroom.
Updated: August 19, 2017