Linux Desktop System Monitor.
GKrellM is a single process stack of system monitors which supports applying themes to match its appearance to your window manager, Gtk, or any other theme.
GKrellM requires gtk 2.0, gdk 2.0, glib 2.0
The gkrellmd server requires only glib (either glib 2.0 or glib 1.2) and may be installed on servers that do not have GTK or Xlibs. See the INSTALL file.
Conky is a free, light-weight system monitor for X, that displays any information on your desktop. Conky is licensed under the GPL and runs on Linux and BSD.
GKrellM for Windows
This is the project page of GKrellM for Windows. The original GKrellM homepage can be found at http://gkrellm.net.