That is also an amx mod addon. you can download amx
HERE Its the addon amx_heal
If you have amx and all that good stuff including the amx heal, then when in your server just type in ur console "amx_heal screenname amount"
Of course no quotes and replacing
name with the user name that you want to give health,
and amount with the amount of life you want to give that user.
If you give 99999999999 it will take a long time to die. Your health bar will go down to 0 if your getting hurt but once you get hurt after that it jumps up to like 170 something. So its almost like god mod. Which can also be downloaded.