Factotum

This is my adaption of MeWiseMagick's feat concept which they have at present stopped working on.  I would link to their page, but DNDBeyond doesn't like that.  Please be warned that this feat lacks polish and has not been play-tested.

You have begun dabbling in the skills and ways of another class, earning the right to ascribe its title to yourself and gaining some of their abilities.  You may take this feat multiple times.  You can only take each classes' Lesser, Standard, Greater, and Prime category once.  After taking this feat once, you can either progress the class you chose last time, gaining it's next set of abilities and features, or you choose another class and start its progression from [Lesser].  Once you have chosen a class, you cannot change it.

When first taking this feat, select any one of the classes from the list below. You must meet the requirements for that class as listed below in the final column. You gain the abilities and features from that class as listed in the [Lesser] column. Upon taking this feat again, can either select another class and gain its [Lesser] abilities and features, or you gain the abilities and features of your first chosen class as listed in the [Standard] column for the same class, the same again with next time with [Greater] abilities and features, and again with the [Prime] abilities and features. You may not select a class you have already taken levels in. The abilities granted function the same as defined in the Player's handbook.

Learning These Feats:

My intention when adapting this feat concept was build versatility at a price, thus a player would need to sacrifice ASI to gain these benefits.  DMs that want to allow their players to train to gain these feats: proceed with caution.

Subclasses:

When the table says that you gain a feature from your subclass, that means you gain the next feature in your subclasses’s progression.  The progression is:

1. Subclass base (all features you gain when you choose your subclass)
2. Next subclass feature (all features you gain at the next milestone of your subclass)
3. Next subclass feature (all features you gain at the next milestone of your subclass) [Fighter and ranger exclusive]

Proficiencies:

Once you have taken the [Standard] feat in a class, you gain the standard proficiencies multiclassing into that class would grant you.

X level Spellcaster:

• The meaning of this verbage is that you are an X level spellcaster in the class whose feats you have taken
• You have the appropriate amount of spell slots for your chosen class at that level
  • This is not true if you have any caster classes outside these feats.  I have Multiclassing info below for your convenience.
• You have the appropriate number of cantrips and spells that you can learn/prepare at that level
• Calculations for number of spells you can prepare is the same as that class’s formula
• Calculate your Spell Attack Bonus and Spell Save DC as outlined in your chosen classes' section in the Player's handbook.

Having a caster class and taking feats here for a caster class:

• Use the Multiclass spell slot table
• Treat your spellcaster levels here as if they are from the actual class (full value)
• If your total spellcaster level exceeds 20, treat it as though it were 20

Multiclassing Information For Your Convenience:

Channel Divinity
If you already have the Channel Divinity feature and gain a level in a class that also grants the feature, you gain the Channel Divinity effects granted by that class, but getting the feature again doesn't give you an additional use of it. You gain additional uses only when you reach a class level that explicitly grants them to you.

For example, if you are a cleric 6/paladin 4, you can use Channel Divinity twice between rests because you are high enough level in the cleric class to have more uses. Whenever you use the feature, you can choose any of the Channel Divinity effects available to you from your two classes.

Extra Attack
If you gain the Extra Attack class feature from more than one class, the features don't add together. You can't make more than two attacks with this feature unless it says you do (as the fighter's version of Extra Attack does). Similarly, the warlock's eldritch invocation Thirsting Blade doesn't give you additional attacks if you also have Extra Attack.

Unarmored Defense
If you already have the Unarmored Defense feature, you can't gain it again from another class.

Spellcasting
Your capacity for spellcasting depends partly on your combined levels in all your spellcasting classes and partly on your individual levels in those classes. Once you have the spellcasting feature from more than one class, use the rules below. If you multiclass but have the spellcasting feature from only one class, you follow the rules as described in that class.

Spells Known and Prepared
You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class. If you are a ranger 4/wizard 3, for example, you know three 1st-level ranger spells based on your levels in the ranger class. As 3rd-level wizard, you know three wizard cantrips, and your spellbook contains ten wizard spells, two of which (the two you gained when you reached 3rd level as a wizard) can be 2nd-level spells.

If your Intelligence is 16, you can prepare six wizard spells from your spellbook.
Each spell you know and prepare is associated with one of your classes, and you use the spellcasting ability of that class when you cast the spell.
Similarly, a spellcasting focus, such as a holy symbol, can be used only for the spells from the class associated with that focus.
Spell Slots
You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels (rounded down) if you have the Eldritch Knight or the Arcane Trickster archetypes. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.

If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare.
You can use those slots, but only to cast your lower-level spells.
If a lower level spell that you cast, like burning hands, has an enhanced effect when cast using a higher-level slot, you can use the enhanced effect, even though you don't have any spells of that higher level.
For example, if you are the aforementioned ranger 4/wizard 3, you count as a 5th-level character when determining your spell slots: you have four 1st-level slots, three 2nd-level slots, and two 3rd-level slots. However, you don't know any 3rd-level spells, nor do you know any 2nd-level ranger spells. You can use the spell slots of those levels to cast the spells you do know and potentially enhance their effects.

Pact Magic
If you have both the spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the spellcasting class feature, and you can use the spell slots you gain from the spellcasting class feature to cast warlock spells you know.

Spell Slots per Level