Developer website: Martian Technology
With LifeBoat, users define "LifeBoats", sets of files and folders that get backed up each time a particular removable media device (USB Flash Drive or External Hard Disk) is connected to their computer. The instant the specified device is plugged into the Mac, Martian LifeBoat automatically begins the backup process.
Users can then disconnect their updated LifeBoats and store them away for safekeeping. Keeping the backups up-to-date just requires plugging the device back into the Mac. Martian LifeBoat takes over from there, quickly updating the external device with a fresh copy of the users' most important data.
*Previously available here