The inspiration for this system, and the explanation of why it should be implemented can be found here. Any time this system refers to what a character would normally be able to do, it is referring to normally while using the flexible spellcaster archetype for prepared casters.

With this alternate system, spell slots and spell preparation are instead replaced with a variant similar to the Flexible spellcasting rules.

Prepared spellcasters can prepare a number of spells each day equal to twice the maximum spell rank they can cast. These spells can be of any spell rank that the character is normally able to cast. Spellcasters with a repertoire retain their normal repertoire of spells. Repertoire casters do not gain additional spell points under this system, instead, having full access to their significantly larger repertoire is itself offset by having a set spell collection. Furthermore, all spells that any repertoire spellcaster knows is treated as a sorcerer signature spell, being able to up heightened at the time of casting without needing to take up an extra repertoire slot.

Additionally, a spellcaster gains mana points each level equal to the highest rank spell they are able to cast.

A spell's mana cost is equal to twice the spell's rank minus 1. Please see the below table

Spellcasters can cast a number of cantrips equal to the number of cantrips they could normally prepare.

Below is a table showing the number of spells per encounter if a character were to spend mana points on only the highest ranked spell available to them

All mana points are regained at the start of an encounter. Any spells currently active count as mana spent for the coming encounter, for example, if a Wizard has a Mystic Armor spell cast at 1st rank, they begin each encounter with 1 less mana point. Additionally, a character can spend 10 minutes resting to regain mana points.

Spells cast outside of an encounter may, at the DM's discretion, not cost mana points.

A character regains all cantrip uses whenever they regain their mana points.

When a non-spellcaster selects a dedication feat, they gain a Mana Pool equal to the sum of the spell ranks they would normally be able to cast. For example, a 4th level character with Sorcerer Dedication, and Basic Spellcasting normally would gain a 1st and a 2nd level spell slot, resulting in a Mana Pool of 3.

If a character gains multiple sources of spellcasting, they use only whichever Mana Pool would be largest. In the example above, if that character was also a Wizard with a Mana Pool of 6, then their total Mana Pool would remain at 6, but would have the additional repertoire of spells available to them from their Sorcerer Basic Spellcasting, along with an extra two cantrips known and per encounter from their Sorcerer Dedication.