This is a Victoria III population rebalance mod. It uses Django to implement it's backend and Flutter for the frontend implementation.
I thought there could be a better way to update the population of the game without breaking the balance (i.e: way too many people in a continent than the other) and maybe try to balance that out to a realistic number to the time, be it in a mod (AD1648, for example) or even the base game. For the mod example, counting the total population in the game, it was put at around 800 million people which is way too much even for the highest estimates, which are around 600 million people at around 1650. Estimates wouldn't reach 800 million soon either, that would take another 100 or more years. As for the population in the base game, you could simply want to try a different amount of people in the world. I believe Paradox did their job well here and pops are already balanced (Estimates go from 1B to 1.2B poeple by the start of the game date), but you never know.
Well, as stated, it helps you balance the game's population. You simply have to upload the files and select the option you want. You can count how many pops are in your game and you can also balance it. All simple to use and in a good looking interface.