The idea for Aegis started around a desire to be able to backup Minecraft server maps with deltas from the last backup, as a way of decreasing space utilization and allowing for more frequent snapshots. While it was intended for Minecraft, Aegis is useful for any data that's comprised of large amounts of file, of which very few change hour-over-hour.
I've had this idea for quite some time and after a lot of false starts, finally getting around to working on it in earnest.