Bit map
Left and right arrows move the bit cursor, Space flips the bit under it.
Type a number into any of the four boxes and the other three follow at once, laid out in nibbles and bytes so the bits line up the way they do on a datasheet. Pick the word size and whether the top bit is a sign bit, then flip, shift or invert bits directly. Everything has a keyboard shortcut, listed in the legend beside the converter (below it on a phone); press Esc to leave a box and the single-letter commands work again.
Left and right arrows move the bit cursor, Space flips the bit under it.