|laziness, impatience, and hubris|
You could write a simple script to copy the file(s) you are working on to a safe place, and append the current data & time to the filename so they are all kept separate. You could even add that script to your cron so it runs every hour or so.
The problem with that approach is that you will end up with thousands of versions of your file, all filling up your disc, and no commit messages to tell you which one contains the edits you are looking for. Far better to create a simple hg or git repository and use that.
One situation where simple copying at frequent intervals might be useful, is if you want to get back from recent editor mistakes where there is no checked in file. On one project I worked on recently, I created a script to put all the files currently out for edit into a time stamped zip file. I had a cron job call that script every ten minutes during working hours.
I used the zip files to get back old versions of the source I was editing, if I realised that the approach to a problem I had spend the last hour on was a dead end, I could easily get back the version from an hour ago.
To be clear this was not a source code version control system, it was just a quick hack to snapshot files that where checked out for edit.
In reply to Re: OT: Does anyone know of a version control system that doesn't use separate files or a repo?