These are some GKrellM 2.0  plugin demos.
Demo4 uses functions first implemented in 2.0.0-pre0.10

for demo1 - demo3, use make:

  make demo1.so;   # Builds demo1.o and demo1.so
  make demo1.test; # Builds and executed demo1

and so on for demo2, demo3, ...

For demo4,
  cd to demo4
  make
  gkrellm -p demo4.so

Demo4 demonstrates theming at the plugin level, run
  gkrellm -p demo4.so -theme test-theme

And then go to the Config->Themes and select the 0 and 1 theme
alternatives.