Hoshi Operating System

Hoshi Operating System icon

Hoshi 星 is an custom hobby operating system for the x86_64 platform. It’s not Linux but it is POSIX-compliant and runs on a custom kernel named Yukiko 幸子. It is written from scratch in C, including the kernel, bootloader, standard library, GUI library and all major components.

Hoshi development started in 2015 and I am not looking for contributors.

Dark theme, various apps, games, taskbar, etc


  • x86_64 CPU.
  • 256MB RAM.


  • boots from an MBR using a custom bootloader.
  • has a Graphical User Interface with APIs.
  • multithreading.
  • has a network stack supporting IPv4 and IPv6, DNS, ICMP, UDP and TCP.
  • custom filesystem named HOFS (Hoshi File System), ISO 9660 filesystem, FAT32.
  • implements the POSIX API using a basic C library.
  • the GNU toolchain (binutils and GCC) can run natively on Hoshi.
  • can be compiled on a modern system using GCC 10.
  • Universal Serial Bus (USB) EHCI and xHCI support.
  • Symmetric Multiprocessing (SMP).
  • audio support and drivers.
  • runs Doom and Quake.
  • has an Internet Relay Chat (IRC) client.
  • has a Mail client with support for POP3 and SMTP.
  • has a custom web browser.
  • has Nyancat.
Basic system information via uname.

Hardware support

  • Graphics: BGA for now.
  • Input devices: PS/2 mouse and keyboard.
  • PCI, VGA text mode, APIC.
  • Storage devices: AHCI and IDE.
  • Ethernet cards: Intel PRO/1000 (82540EM / 82545EM) and AMD PCNet (Am79C970A / Am79C973).

Boots and runs on bare-metal and VirtualBox, QEMU or VMware.



  • Coreutils written from scratch.
  • Text file editor.
  • Akari, the code editor with syntax highlighting.
  • Internet Relay Chat client. screenshot
  • Painter, painting application.
  • SysInfo, reporting various system information. screenshot
  • Mail client.
  • Terminal.
  • Calculator.
  • Font viewer.
  • Image viewer with support for BMP, PNG and JPEG.
  • Notes, todo and contacts.


  • httpd
  • echo
  • sshd
  • ftpd


Everybody loves Pacman!
  • 2048
  • Mines
  • Tetris
  • Breakout
  • Doom
  • Space Invaders
  • Pacman
  • Quake
  • Memory

Akimitsu GUI controls

  • Buttons
  • Check boxes
  • Combo boxes
  • Images
  • Menus
  • Progress bars
  • Radio boxes
  • Scroll bars
  • Tabs
  • Text fields
  • Toolbars



Akimitsu 昭光 is the GUI compositor and window manager.


HoSH is the simple POSIX-compliant Hoshi shell.


Keiko 恵子 is the network manager.


Masashi 雅志 is the bootloader.