BMPanel (bitmap panel) is nice, lightweight, NetWM-compatible panel for your
X11 desktop.  It currently features:

  - Look'n'feel customization via themes (20 of them included)
  - A bunch of widgets: desktop switcher, taskbar, launchbar, systray,
    clock, decor, empty (unofficial temperature widget also available)
  - Pseudo (default) and compositing (optional) transparency support
  - Written in C with speed and clarity in mind
  - Small number of dependencies, briefly: glib2, cairo, pango, libX11
  - Small memory footprint (about 2-4 megabytes)
  - Small executable (80 kilobytes at the moment)

WWW: https://code.google.com/archive/p/bmpanel2/