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World's Smallest Operating System

CrypticOS is an operating system mostly written in a custom bytecode, which can be emulated anywhere.


  1. Any program should be loaded on any emulator, and run perfectly.
  2. X86 bootable should be usable within 256 bytes.
  3. "Make it simple, and keep it simple"


  • Yes, this is a hobby project, mainly for keeping me sane in 2020/2021 during the lockdowns.
  • Yeah, it sucks. It's way worse than DOS and runs on an obscure BrainFuck clone.
  • The custom bytecode has 16 commands. It's mostly BrainFuck, but with some extra things that make it easier to write operating systems with (insane idea)
  • That being said, I recommend you don't make another BrainFuck clone. You'd be better off making another memory-safe general-purpose systems programming language, and rewrite every major piece of software in it.


  • Write OS in <512 bytes
  • Write simple programs for it
  • Write assembler that compiles to it (casm)
  • Write operating environment in the assembler
  • Self host the assembler or make a C compiler


Install CASM assembler (for main test binary)

make b_casm

Note: Make sure you are in the x86 directory.

Main test binary

sudo apt install qemu-system-x86 nasm
make b_x86

Try: !%***.
Also try !% to load the edit app. Press ESC to exit.

256 byte Version

Very basic. Type !%***. and enter to test it out.

cd x86 && make tiny

So what does it do?

CrypticOS uses a BrainF* inspired esoteric language as its main runtime.
It is different in many ways, mainly with logic and loops. In design it should
have the simplicity of BrainF*, but be more usable, efficient, and Assembly-like.

You can see the full specification in standard/