Vax VMS had a nice feature where you could save files as "fred.txt" and it would save it as "fred.txt;1" then the next time you save it, it automatically increments the version so you have "fred.txt;2" etc. You could load an old version with "fred.tx

You would need to intercept the file files api methods, and make them return the base name only (but it would allow you to access older files inside programs by adding ;1 at the end of the filename).