XChat is easily the most popular of the X11 clients - it’s lightweight, scriptable in multiple languages, and has sensible defaults. XChat is an open source project developed under the GPL, and although primarily developed as a Unix/Linux client, ports exist for other platforms.
XChat supports a binary plugin API, in which addons can be written in C or C++, and several scripting languages including Perl, Python, TCL and others are supported through the plugin architecture.
XChat is included in a number of Linux distributions, either as part of the base system or as part of official package repositories.
Official Windows Port
XChat has long offered an official Windows port. Originally, the Windows version was freely distributed, but since 2004 the official builds have been offered under a shareware license, even though the source code remains freely available under GPL.
Unlike users of Linux and other Unix-like operating systems, the majority of Windows users do not readily have access to development tools, or have the technical know-how to build a program designed for X11 as a native Windows application. Most Windows users therefore have to rely on the developer or third parties (see below) to distribute binaries.
Unofficial Builds, Ports and Other Derivatives
Controversy over the devision to license the Windows port of XChat as shareware led to a number of unofficial builds for Windows users, at least one of which grew into a fork of XChat.
HexChat originally sprung out of the shareware controversy, starting as the unofficial Windows port XChat-WDK, which was renamed HexChat and became a fork in its own right.
HexChat is now offered on Unix/Linux systems as well as Windows. HexChat has become the more actively developed than XChat while maintaining close compatibility, with frequent releases and new features.