Pyromaniac

Pyromaniac is a Fallout 2, Fallout 3, Fallout: New Vegas, Fallout Tactics as well as Lionheart perk. It is a skill Fallout: Brotherhood of Steel and was to appear in the canceled Fallout: Brotherhood of Steel 2 (skills in these game work like perks do in other Fallout games).

Fallout 2 and Fallout Tactics
In Fallout 2, the most violent fire-based death animation will always be used, similar to that of the Bloody Mess trait.

Fallout 3
With the Pyromaniac perk, you do +50% damage with fire-based weapons, like flamers and Shishkebabs.

Affected weapons

 * Shishkebab
 * Flamer
 * Firelance
 * Heavy incinerator
 * Rapid-torch flamer
 * Slo-burn flamer

Bugs

 * The Burnmaster, the Nuka-grenade, and the Zhu-Rong v418 Chinese pistol are unaffected by the perk. The guide lists these as being affected by this perk, but the weapons aren't on the form list - this is most likely an oversight by the developers.
 * Any flamers that are brought back by the Gary-23 glitch from Operation: Anchorage are also unaffected. The reason for this was probably because weapons from the expansion were not meant to be brought back, thus they are not affected by this perk.

Fallout: New Vegas
With the Pyromaniac perk, you do +50% damage with fire-based weapons, like the flamer and Shishkebab.

Affected weapons

 * Flamer
 * Shishkebab
 * Incinerator
 * Heavy incinerator
 * Incendiary grenade
 * Fire bomb
 * Sonic emitter - tarantula
 * Sterilizer glove
 * Saturnite fist super-heated
 * Gehenna
 * Cleansing Flame

Affected ammunition

 * .50 MG, incendiary (burn damage only)
 * 40mm grenade, incendiary
 * 12 gauge, dragons breath

Bugs

 * While this perk requires an Explosives skill of 60 to be unlocked, the only explosive items affected by the perk are the 40mm grenade, incendiary, the incendiary grenade and the Fire bomb. This was confirmed by J. E. Sawyer to be unintentional; the perk was meant to be dependent on the Energy Weapons skill, which governs almost all fire-based weaponry.
 * This perk does not affect the flare gun or the cosmic knife super-heated, despite both weapons being capable of setting enemies on fire.

Fallout: Brotherhood of Steel
Each level of this skill increases the player characters Critical Chance for +5% (up to a maximum +25) when using fire-based weapons.

Points requirements

 * 1 Rank : 2 Points
 * 2 Rank : 4 Points
 * 3 Rank : 8 Points
 * 4 Rank : 16 Points
 * 5 Rank : 32 Points

Affected weapons

 * Burning gloves
 * Torch
 * Flamethrower
 * Incendiary mortar
 * Incendiary grenade

Fallout: Brotherhood of Steel 2
Unspecified, but presumably 5%, increase in Critical Chance when using fire-based weapons.

Lionheart
You have a natural affinity for fire and a knack for setting things ablaze - especially other people. You get +10% damage with fire-based weapons or spells.