Fuckgoid

Fuckgoid is the fungoid with the smallest interpreter, by User:None1.

Commands

It is Befunge-98, but there are only 4 commands: <>^v which works the same. When the IP goes out of bounds, it wraps back.

An empty program is an infinite loop, characters that are not commands are NOPs.

Interpreters

brainfuck

+[]

It is easy to prove that this interpreter is always correct.

Self interpreter

N

Infinite loop (esolang)

Shorter than in bf.

[]