Register Automaton

Register Automaton is a simple esolang invented by User:A which only has 1 instruction:

@x=y?Lx

Explanation

Flip cell x. If that content is equal to the content of cell y, go to line Lx.

Example

@0=1?L100
@1=0?L0

It is an infinite loop, changing cells 0 and 1 forever.

Computational Class

Since a program can only access the cells mentioned in it, which are bit valued, there is no unbounded memory. Register Automaton is therefore at most a finite-state automaton.