BurgerDisk is a Smartport hard drive for the Apple II. Its main unique feature is that it is daisy-chainable.
As all Smartport SD-based hard drives, it's more adapted to the non-slotted Apple II, like the //c and IIgs.
Here are a couple pictures of the finished device:
The project's homepage...
Your first question in probably: Why make another Smartport SD hard drive?
The answer is: to finally have a daisy-chainable hard drive, and also free software / open hardware.
BurgerDisk, like the SP2SD, is based on SmartportSD. It fixes two bugs in its firmware (too slow init to be visible...