Google Drive contains many Apps that can be directly embedded into Google Sites.
Available from the "Insert > [Google] - Drive" Menu you have :
Creating Google Apps Script directly is also available in Google Drive.With Google Apps Script you can automate the creation of all Google Drive main applications and even connect then to Google Sites or even access Google Drive data for display in Google Sites etc..
Google Drive forms can be also used for survey contact or trigger advanced Cloud scripting via Google Apps Script etc..
Spreadsheet embedded in Google sites can be edited directly this can useful when creating and maintenance through Google Sites.
Sharing files via a Folder in Google drive , which then can be visible to a selective audience or even made public.
Permissions can be set both on Google Drive and on Google Sites.