The HHKB or Happy Hacking Keyboard layout was
invented by Dr. Eiiti Wada as the ideal layout for computer programmers.
The HHKB layout replaces the 1.75u Capslock with a 1.75u Control key, breaks up the 2u Backspace into a 1u \ key and 1u ~(sometimes delete) key, breaks up the 2.75u right shift into a 1.75u right shift and a 1u Fn(function) key.
The bottom row of a HHKB is essentially a Tsangan bottom row with the outer 1.5u mod keys removed.