hexcalc

Live code: https://hughjackson.github.io/hexcalc/

Live beta: https://hughjackson.github.io/hexcalc/beta.html

In the beta version you can use normal keyboard input with following support:

0-9 A-F             : as expected
= Enter             : = key
Del Backspace #     : Del key (backspace)
M                   : Toggle display mode (dec/hex/bin)
P                   : Toggle Numpad/Binpad