DevCalc
The programmer's calculator, with a paper ribbon.
Decimal, hexadecimal and binary on iPhone, with a scrolling ribbon that keeps every step of your work.
calcdechexbin
Four modes, one keypadDecimal arithmetic in calc, then unsigned integers in dec, hex and bin. Only the digits of the active base are offered, so a typo is impossible.
32 or 64 bits, honestlyExact UInt64 words, masked to the chosen width. Additions and subtractions overflow modulo 2^N, and NOT flips exactly N bits, like the machine you are writing code for.
A ribbon that remembersEvery operation is printed. Scroll back, tap a result to bring it back into the entry, or long-press to copy it. Switch base and the whole ribbon is reformatted without losing a single bit.
Display, your wayfull, float or fixed, each with its own precision from 0 to 12 decimals. Decimal and thousands separators follow your region, or a pairing you choose yourself.