The flamethrower is only available to Jango and Boba Fett. The flamethrower shoots a stream of fire at the opponent, taking out their health slowly but surely. Even if an opponent is barely caught by this trail of heat, they will catch on fire and burn for at least a few seconds, nearly depleting their strength.
The Bothan Spy's Incinerator is very similar to this weapon. The flamethrower doesn't have much ammo and reloading is frequent, but it is a very effective weapon, especially for taking out crowds of enemies.
In Renegade Squadron the flamethrower can be used by any unit through Customization, Jango and Boba Fett still have the weapon and can use it. The weapon now has unlimited ammo.