Dungeons and Dragons may be making its way into the mainstream, but it's still fairly niche as a hobby.  An optional rule from the 2014 5e Dungeon Masters Guide (the least owned of the 3 core books) that wasn't included in the revised 2024 core book of the same name?

Now that's a deep cut.

Honestly, "Spell Points" (said optional rule) is a fun mechanic if you like crunching numbers and they attach to various fantasy genres more easily.  You cast leveled spells the same way, except that spells cost points.  Your total pool is dependent on your casting class and level.

This spell point tracker was mostly made for the character I'm currently playing in a group game.  I asked the DM if I could implement this optional rule and he was obliging.