I’m using Gkrellm for a long time now (perhaps 5 or more years). The main issue with Gkrellm is that theme aren’t really fresh anymore. So I tweaked some to feet with my needs.
As you can see on the screen-shot this theme is a transparent one, with a blue and violet krells
You can download it here : gkrellm-themes-invisible-jkx
/ Enjoy the dark side of the desktop :)