Basic logic is also important - understanding symbolic logic, and methods of proof (direct inference, proof by contradiction, induction, etc.) also prove important.
I have had to use basic trigonometry in the past as well, and linear algebra (for CSS rotations/translations driven by JS).
Algorithmic number theory, closely related to algebraic number theory, drives cryptography.
Harmonic analysis drives audio.
Algebraic geometry powers facial recognition software.
The list goes far deeper, but I have been away from the math world for 6 years & have forgotten much.