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Microwindows or the Nano-X Window System

Microwindows or Nano-X is a small graphical windowing system that implements both Win32 and Nano-X (X11-like) APIs for clipped graphics drawing in windows on Linux, Mac OS X, EMSCRIPTEN, Android and other platforms. It is Open Source and licenced under the the Mozilla Public License. For creating GUIs, the Nuklear immediate mode GUI, Win32 builtin controls, and TinyWidget's controls based on Nano-X are included. FLTK can be used with the X11 compability library NX11.

This is a slightly outdated overview of the system:


Some of the supported platforms are listed at the bottom on the left side. Next to that there are available screen drivers, mouse drivers and keyboard drivers. The Nano-X / Microwindows engine is the core code that implements all drawing and clipping, with the Win32 and Nano-X graphical windowing APIs implemented in seperately configurable layers on top of that. The engine is configured to use various OS platforms and associated screen, mouse and keyboard drivers, or bare hardware. The Nano-X API and the Win32 APIs are used to write applications. To provide close X11 compatibility the NX11 library can be built on top of the Nano-X API, which allows X11 applications to be linked and run without recompilation. The FLTK GUI toolkit runs based on NX11.

Areas where Microwindows can be used are:

  • NEW: Microui immediate-mode UI library port to Nano-X
  • NEW: PDF viewer and MP4 media player support on Nano-X through FBPDF and FBFF projects
  • NEW: updated Nano-X window frame drawing code resembles Nuklear UI
  • NEW: Nuklear immmediate-mode GUI apps now supported in seperate windows
  • NEW: run multiple simultaneous Win32 apps on Linux, OS X and in a browser
  • original classic shareware Doom v1.10 ported to Nano-X
  • run X11 or Win32 applications in a browser using EMSCRIPTEN
  • provide an excellent GUI for small embedded devices with FLTK, TinyWidgets or Win32
  • port the FLTK GUI toolkit to small platforms
  • linking an application with Microwindows can provide it with a GUI on console based Linux distros
  • provide Xlib support for platforms without Xlib
  • run FLTK or Win32 applications on Android phones
  • Portrait and Landscape modes and auto-flipping are supported for handheld devies


Microwindows is very portable, is written in C and can be used on a wide range of platforms.

Currently supported platforms include Linux, Mac OS X, Android, EMSCRIPTEN, Nuklear GUI, Windows, Raspberry Pi, DOS DJGPP, RTEMS, ECOS, Sony PSP, Atari Jaguar, Nintendo DS and more.

Currently supported screen drivers include Memory-mapped framebuffer, X11, SDL 2, Allegro 5, Windows and an X11 based framebuffer emulator.

Support for cross-compiler toolchains on x86, x86_64, ARM, M68K, PowerPC and MIPS, big- and little-endian, and other processors.

Library design

The Nano-X Window System has a layered design. At the lowest level there are drivers for screen output as well as mouse and keyboard input. Touch input devices are also supported. Drivers are available for X11, frame buffer, SDL, the Allegro graphics library, VESA or the SVGA library. Additional drivers can be added to port Microwindows to more platforms.

At the mid level, a portable graphics engine is implemented, providing support for line draws, area fills, polygons, clipping and 1, 2, 4, 8, 15, 16, 24 and 32 bit color models.

At the upper level, the Nano-X/NX11 and Win32 API's are implemented providing access to the graphics applications programmer.

The Nano-X Window System can be compiled either as a separate server for several clients or linked together to a single, standalone library.

Web site

The main Nano-X web site is at


To build Microwindows, see microwindows/src/README plus the faq files in the doc directory. For Android there is an application note in the doc directory. The Atari Jaguar requires a specific treatment.

An HTML based FAQ and Architecture document are available from the web site.


AGG Nuklear Emscripten FLTK Doom AJaguar


The chief maintainer of the project is Greg Haerr

Microwindows and Nano-X are discussed on the NanoGUI mailing list. Mailing list archives are available at: