X11's fundamental concept is that of the server and client. The server is the program which manages the graphics display, and clients are programs which connect to the server and (usually) request graphics to be displayed. X11 uses a protocol, the X Protocol that allows communication between the server and clients to be encapsulated in nearly any type of network protocol that provides a reliable two-way byte stream (eg TCP, Chaosnet, DECnet, Unix sockets). As such X is network-transparent, and clients can execute on host computers separate from the computer which hosts the server.
The X Protocol is language-independent. The primary implementation is in a weird object-oriented-ish form of ANSI C, but the X Protocol can be implemented in nearly any programming language. As such, Common Lisp has its own implementation of the X Protocol, called CLX.
MIT has long since let go of X, and it is now officially maintained and standardized by X.Org (formerly by the MIT X Consortium, then by The Open Group). Many different implementations of X exist, each typically supported by a particular Unix vendor. However the original source code for X was and continues to be freely available.
- CLIO - Common Lisp Interactive Objects (CLIO) is a set of CLOS classes that represent the standard components of an object-oriented user interface --- such as text, menus, buttons, scroller, and dialogs
- CLX - CLX provides an implementation of the X Window System protocol to Lisp graphics library[ies] and applications
- CLXS - CLXS is an early-stage implementation of an X11 server (the part that does the drawing and keyboard/mouse handling) in Common Lisp
- cxml-rng - Relax NG for Closure XML
- deflate - Deflate by Pierre Mai is a Common Lisp implementation of Deflate (RFC 1951) decompression, with optional support for ZLIB-style (RFC 1950) and gzip-style (RFC 1952) wrappers of deflate streams
- eclipse - Eclipse is an X11 window manager written entirely in Common Lisp
- image - Image is an image-drawing library with a few drawing primitives (circles, ellipses, lines, rectangles, text)
- incf-cl - (INCF CL) is a collection of utilities
- plexippus-xpath - Project name:
- sha3 - This library is an implementation of the Secure Hash Algorithm 3 (SHA-3), also known as Keccak
- stumpwm - StumpWM is a tiling, keyboard driven X11 window manager application written entirely in Common Lisp
- tinywm-lisp - tinywm-lisp is a Common Lisp port of the TinyWM X11 window manager
- XIT - A graphics toolkit from the University of Stuttgart which provides an object-based interface to the X11 window system, based on CLX and CLUE
- xuriella - Xuriella XSLT is an implementation of XSLT 1.0, written entirely in Common Lisp
- zen - zen is a hackable X server written in Common Lisp