R + S

R+S is a very simple esoteric programing language.
It is reversible and can't be turing complete because it cant have infinite memory.

its only memory is a finite width register of some arbitrary amount of bits

Instructions:

+ increments the value. (wrapping)
R rotates the value left by 1.
Sswaps the first and second bit of the value.

the S instruction is redundant, it can be replaced by xors and rotations.

8 bit Example programs:

Rotate Right

RRRRRRR

Invert bit 1

R+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++RRRRRRR

Bit 2 = bit 2 xor bit 1

RR++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ RRRRRRR+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++RRRRRRR