The Bubbling Load Monitor (or "Bubblemon" for short) is a system CPU and memory load monitor.
It displays something that looks like a vial containing water.
The water level indicates how much memory is in use. The color of the liquid indicates how much swap space is used (watery blue means none and angry red means all).
The system CPU load is indicated by bubbles floating up through the liquid; lots of bubbles means high CPU load. If you have unread mail, a message in a bottle falls into the water.