Anger Adept

Special Feat (Prerequisite: You must be granted this feat by a subclass that has access to a specialized Rage effect, and cannot learn it normally).

This feat includes three parts: Anger Adept, which provides options for multiclassing, Vicious Voice, which is a constraint on how you can cast spells while using your specialized Rage effect, and Wanton Wrath which prevents you from benefitting from Careful Spell metamagic or similar benefits. 

Anger Adept. You are a spellcaster that has access to a specialized form of Rage (like Arcane Fury, or Shred), and you share progression and resources with other sources of that class feature. Your class levels in the class that granted you this feat stack with any class levels in Barbarian, or other classes that also grant this feat for the purposes of determining your number of uses and damage bonus.

Your Rage and specialized Rage uses are a shared resource, so expending one means you have one less of the other. As a bonus action you can switch between Rage and your specialized Rage effect without consuming an additional use, but the combined duration of your continuous Rage effects share the same 10 minute maximum total.

While using Rage (but not a specialized form of Rage) you may use your spellcasting modifier for Attack Rolls and Damage on melee attacks, and you may maintain concentration on a spell that you would have been able to concentrate on while under the effects of your specialized Rage effect. You may only use your Rage or specialized Rage effect separately; they do not stack except as described above.

Vicious Voice. When casting spells while using a specialized Rage effect, every spell you cast has an added verbal spell component--the higher the spell level, the louder the verbal component, from rumbling growls when you cast cantrips to bloodcurdling shouts at the top of your lungs when you cast your most powerful spells. If concentrating on a spell, you must continually renew this verbal component every turn that you maintain concentration, or lose your concentration. You have Disadvantage on Stealth checks to conceal your spell casting, and if you end your turn under a silence effect (as the spell or by being physically prevented from performing) you immediately lose your ongoing specialized Rage effect.

Wanton Wrath: If you have a class or feat which grants you access to the Sorcerer's Metamagic "Careful Spell", you must discard that option and swap it for a different valid option. You may never use or learn the "Careful Spell" Metamagic option, or benefit from a similar effect granted through other means. Woe betide the foe--or friend--caught in your crossfire.