Oops worked it out,
index.php?c=backup
Click the link "Missing lang: start backup"
Maybe fix the language files if you can work that out, otherwise don't need it often enough to matter.
I'm not sure if mine worked, I have about 250mb of files on server and I know that I can not use tar gzip to zip it all up as I get memory limit errors.
I end up with two zip files in /tmp/backups/
One is opengoo_backup.zip
The other is opengoo_backup.zip.ASDFGFG (random stuff).
They are different sizes.