BreatheBar
This is a fully trivial console bar that raises (to the right screenside) and lowers in a special frequency. If you are familiar with HRV-Techniques (english or german) you probably know what this is all for.
Eventhough i have no direct measured feedback this changing bar helps me to stabilize respiration frequency at 0.1 Hz.
Sources:
Packages (via software.opensuse.org):
e.g. for openSuSE 10.3 on
http://download.opensuse.org/repositories/home:/fseidel/openSUSE_10.3/