These are toy implementations around small, esoteric languages, written in Go.

A language built around string substitution.

https://en.wikipedia.org/wiki/Thue_(programming_language)

a::=hello
hello::=~Hello from Thue!
::=
a

github.com/jmhobbs/little-machines/thue is an interpreter

usage: thue [options] <program file>

  -print-state
       print the state when execution stops

A small language with only 8 commands, encoded as the characters >, <, +, -, ., ,, [, and ]

https://en.wikipedia.org/wiki/Brainfuck

++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.

github.com/jmhobbs/little-machines/brainfuck/cmd/bf is an interpreter

usage: bf [options] <program file>

  -memory-size uint
       number of memory cells to use (default 300)

github.com/jmhobbs/little-machines/brainfuck/cmd/bf2go takes a program on stdin and converts it to Go source on stdout

usage: bf2go [options]

  -memory-size uint
       number of memory cells to use (default 300)

Ook! is identical to Brainfuck, but the instructions are "Orangutan" words (i.e. Ook! Ook?)

https://esolangs.org/wiki/Ook!

github.com/jmhobbs/little-machines/brainfuck/cmd/ook is an interpreter

usage: ook [options] <program file>

  -memory-size uint
       number of memory cells to use (default 300)