Here is a complete list of Skyline file types:

• .sky - the main Skyline document file
• .sky.view - contains state information about the Skyline UI when the .sky file was last saved, e.g. selection and window layout - can be deleted
• .skyd - contains all the chromatograms and the complete set of peak statistics (generally 10 per chromatogram) considered by Skyline
• .skyl - the Skyline audit log file
• .blib - a Skyline native spectral library
• .slc - a "spectral library cache" created to improve initial spectral library load performance - can be deleted and Skyline will simply recreate it
• .irtdb - a Skyline iRT library file
• .optdb - a Skyline optimization library for CE and CoV optimization values
• .protdb - a background proteome file
• .imsdb - and ion mobility library (coming in 20.2) which stores ion mobility and CCS values
• .midas - a spectral library file for spectra from SCIEX MIDAS runs

External library types:

• .hlf - X! Hunter spectral library from theGPM
• .sptxt - SpectraST spectral library from the TPP
• .msp - NIST spectral library

But don't try to understand all of the above just to share a complete Skyline document/project with others, instead use File > Share or Upload to Panorama to create a:

• .sky.zip - a compressed ZIP archive which contains the full set of files required to share your document/project

Exported files not associated with the .sky file:

• .skys - a Skyline settings file which can be imported into a menu item on the Skyline Settings menu
• .skyr - a Skyline report template file which can be imported back into Skyline to add report templates to the available set
• .skyp - a new Skyline "pointer" file that can be downloaded from Panorama very quickly and will then initiate a full download inside Skyline when opened