FX-602P Programmable Calculator is a programmable scientific calculator based on the FX-602P. See the FX-602P website
or blog
for details

CalInverse is calculator with modular arithmetic and theory of numbers.
Functions include:
*Greatest common divisor (GCD) (Euclidean algorithm);
*Least common multiple (LCM);
*Bezout's lemma;
*Modular multiplicative inverse;
*Chinese theorem for a system of 2, 3, 4 equations.
The program does not require access to the internet.