xlibtrace displays the interaction between X11 client programs and the X11 client shared library (libX11.so) by showing the Xlib calls that are made. Output is shown in a style similar to strace(1). It works by using the $LD_PRELOAD dynamic linker option to insert itself between the target X11 client program and libX11.so. This allows it to "intercept" all calls to X functions, whereupon it has the opportunity to print the name of the function being called, along with any arguments and return value. This can be particularly useful when analyzing the behavior of closed-source X11 programs.
xlife is a laboratory for experimenting with cellular automata. It supports loadable rulesets and palettes, different topologies, and up to 256-state cellular automata. It has rules and patterns for Life, Brian's Brain, Perrier's Loops, Langton's Ants and Loops, Wireworld, E.F. Codd's 1975 UCC automaton, some Prisoner's Dilemma games, and many others. It is very fast for step-by-step mode, bounded grid, and chaotic patterns. It has several unique features: a historical mode, a pseudocolor mode, and n-state statistics. It has been developed since 1989. The modern version of Xlife began its history in 2011.
xllmnrd is an IPv6 LLMNR responder daemon (primarily for GNU/Linux operating systems). It allows Microsoft Windows clients to get the IPv6 address of a server on the same local network without any DNS configuration and effectively complements IPv4-only NetBIOS name resolution provided by Samba.
xml-HTB is a tool for automatic generation of bash scripts that sets up HTB on Linux. It uses XML configuration files. It's easy to use, and features multiple depths of classes, configurable leaf, u32 and fw filters, and the ability to configure both the input and output interfaces at the same time.