This is a simple addon that pulses the edge of your screen when you get low on health or mana. It is similar to what X-Perl does (so if you use X-Perl, no need to install this). The textures are the same textures as the aggro and mind control warnings.
The configuration options are in the LUA file and will allow you to adjust the percent at which the mana and health warnings are displayed (as well as disable each).
cfg.healthWarningPercent = .25 -- The percentage to start warning about health (0.0 to 1.0)
cfg.manaWarningPercent = .25 -- The percentage to start warning about mana (0.0 to 1.0)
cfg.showHealthWarning = true -- True to flash when health reaches the set percentage
cfg.showManaWarning = true -- True to flash when mana reaches the set percentage