.IBPLUGIN File Extension
File TypeInterface Builder Plug-in
What is an IBPLUGIN file?
Plugin file used by Interface Builder, an Apple development tool used to design software interfaces; contains data and functions that add new features to the tool; may add new menu items, custom views, or other features.
IBPLUGIN files are actually folders with the ".ibplugin" extension. To manually view their contents, remove the extension and open the folder.