There is only one file type that uses the .XCSNAPSHOTS extension:
Project snapshot file created by Xcode, a Apple's development IDE for Mac OS X and iOS applications; contains all saved states of a development project, including resource files, source code, and project settings; can also include developer notes for each saved state; used for storing recovery checkpoints for a project.
Xcode snapshots are often used to save project states when submitting software to Apple's App Store. This helps developers track reported bugs against a specific version of the source code, and it also gives them a source code checkpoint for comparison when developing new features.
You can create a snapshot from an open Xcode project by choosingfrom the Xcode application menu. You can view your snapshots in the Xcode Organizer window by selecting the Projects tab. Click the Restore Snapshot button to restore a snapshot.
XCSNAPSHOTS files are saved to the ~/Library/Developer/Xcode/Snapshots/ directory. Each snapshot file is specific to an Xcode project and contains all created snapshots for that project.
NOTE: Snapshots were introduced with Xcode 4.
Updated: March 10, 2015