CPUMon is a simple desktop gadget which can plot CPU usage and display free and used RAM in real time.
One highlight of the program is the efforts it makes to stay out of your way. It's tiny, transparent, and even passes your clicks through to the application underneath.
Although by default CPUMon is free floating, it can be set to fixed positions and locked to prevent changes.
Visuals tweaks include control over transparency, alpha blending, colours and more.
It's hard to get excited about PC performance monitors, especially as Windows has an excellent one of its own (Ctrl+Shift+Esc and click Performance). But CPUMon's transparency and click-through window mean it does better than most at staying out of your way. Take a look.