.XCSNAPSHOTS File Extension
What is an XCSNAPSHOTS file?
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 choosing File → Create Snapshot... from 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.