How do I convert simple non source controlled project backups into a versioned git repository?

You can use example git-fast-import based tools distributed in git.git repository: import-zips.py (in Python) or import-tars.perl (in Perl), or use those script as a base of your own import script. You can find those scripts in contrib/fast-import/ directory.

There might be an already automated way of doing this, but git should be smart enough to let you git init in your oldest backup and then repeatedly copy the .git folder to incrementally newer backups and create a commit with everything for each one. Scripting this should be pretty easy.

Even better, you could pass a --git-dir= option or $GIT_DIR environment variable to git and have it use a repository, saving the copying step.

Something like this:

cd $FINAL_DIR
git init

export GIT_DIR=$FINAL_DIR/.git

cd $NEXT_BACKUP
git add -A .
git commit
# rinse and repeat

I don't quite know why you don't want to just commit all snapshots individually. I mean, a shell script (or Perl, Python, Ruby, Tcl, whatever) to do that, is probably less than 5 lines of code and less than 10 minutes of work.

Also, there is git load-dirs, which would allow you to cut that down to maybe 3 lines and 5 minutes. But you still have to load every dir indvidually.

But, if you are so inclined, there is the git fast-import tool which is intended to make writing repository converters and importers easier. According to the manpage, you could write an importer in about 100 lines and a couple of hours.

However, all this ignores the biggest problem: the value of a VCS lies not in the contents – you could just as well use regular backups for that – but in the commit messages. And no magic tool is going to help you there, you'll have to type them all in yourself … and more importantly, you'll have to remember exactly why you made every single little change over the last years.