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.

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.