xopus is a browser-based (Mozilla, IE) in-place WYSIWYG XML editor. It works similarly to a word processor, and uses XSLT stylesheets to transform the XML to user-presentable HTML and XML Schema to preserve the XML validity. A commercial version with table, rich text, and enumeration editing is available as well.
xoris grabs the RGB color value of any pixel on the screen and dumps the color's name to stdout. The output can be printed either as hex (#b0958e), as a triple of decimal RGB values (229 229 229), or as an abstract name (gray90). xoris has only been tested on displays with a bit depth of 24 bpp.
X Persistent Remote Applications (xpra) is "screen for X". It lets you run applications remotely (like ordinary X or VNC), but unlike ordinary X, these applications are "persistent" if you lose your connection, or even if you want to switch to another computer. Also unlike VNC, they are ordinary applications on your desktop managed by your window manager, not trapped in a box.
xremote is a simple tool that lets you grab the mouse and keyboard of another machine and control them with your local mouse and keyboard. It creates a form of remote control of other machines. All mouse- and keyboard-actions on the local machine are forwarded to the remote display.
xsysguard is a resource-friendly system monitor based on Imlib2. The main features include a powerful configuration file format, full alpha channel support, configurable widgets, and many data sources implemented as modules. For example, the daemon module allows you to monitor remote machines, and the file module can parse files with scanf or regular expressions.