A simple system monitor for tracking memory usage.
The displayed "max", "total" and "free" memory is obtained from the Java
Runtime API, and its meaning is not immediately obvious:
In simple terms of "available" and "used" memory
one can consider "max - total + free" the available memory,
but the behavior of the JVM's garbage collection is very unpredictable:
It will sometimes hold on to memory that was freed after closing some part
of the application, while at other times such memory shows up as free
right away.