This is a revised 1.1. version. Thanks for JJKM for ideas. Also +Brett Slocum that morale is written with an "e".
The men and women who have battle running through their veins as from their birth they learn the ways of their tribe and culture. Endless wars between rival tribes and pillaging expeditions to far away lands make barbarians tough and ruthless. From deepest rainforests and their amazonian woman tribes to northern vikings barbarians all share a common feature: fearlessness of death.
All barbarian abilities need him to wield two-handed magic weapon.
Once a day per 4 levels a Barbarian Berzerker can fall into a rage. In rage his bloodthirst makes him a killing machine of deadly blows but makes him an easier target. In a rage Barbarian Berzerger gains damage bonus equal to his level but suffers 4 penalty to AC.
As fierce warriors barbarians also have intimidating gestures to make their opponents to flee. Once per day for every 3 experience levels barbarian can taunt as many opponents in HD as his level is. Taunted opponents must success a *moral roll or they flee.
Example: A 5th level barbarian has two taunts per day (one from levels 1 to 3 and second from levels 4 and 5). He has opponents varying from 1HD to 3HD and he decides to taunt the 3HD and two 1HD's. Two fail the moral check and flee.
Additional Attack (from Three Swordsmen)
At 3rd level, barbarians may attack two times a round using a two-handed weapon, but this secondary swing is granted only once per day. At 6th level, barbarians may use this ability twice per day, and thrice at 9th level. Upon reaching 12th level, they receive two attacks every round.
*Moral check. If your game doesn't have morality rules it's a simple rule to apply. Monsters have morality values of 2-12 (where 2 is worst) and when taunted (or badly wounded, half of the enemies are fallen etc.) 2d6 is rolled. If the roll result is higher compared to the morality score the enemy flees.
Peasants might have a morality of 4, seasoned thugs 8 and demonic entities 12. Mindless, controlled, constructed etc. monsters might not have moral at all thus cannot fail the test.
When a barbarian has suffered more damage in total than half of his HP he may choose to fall into a rage. He has an option to gain bonus to hit and to damage maximum of his level - or less if he chooses to - in equal cost of his AC. The rage lasts as long as the barbarian is alive, the fight is over or his HP is restored over half of the maximum.
Example: A 5th level Barbarian has suffered enough damage to fall in rage. He can gain a +1 to +5 bonus to hit and damage and decides to go full-out with +5. Because blinded by rage and recklessly attacking his opponents he suffers a penalty of 5 to his Armor Class. As unarmored his (descending) AC 9 is now 14.