This file from Leland Leahy contains three functions designed to enhance the autosave functionality in AutoCAD by providing you with extra backup copies of your working drawing. Sometimes, by the time you find a drawing is corrupt, the BAK and autosave files may also be corrupt. This routine creates multiple copies that will not be overwritten. Start by loading the LISP file, then run the command IncSave. It will ask you if you want to enable the features of this tool. After you answer with Yes, any future execution of the IncSave_Save function will save a copy of the current drawing to a subdirectory named IncSave.
There is also a function named IncSave_Clean that will clean any files older than four days old out of this directory. Notice that IncSave_Save and IncSave_Clean are not defined as type-in commands. These functions should be added to an existing command shortcut that you will execute often anyway.