The draw of Sim Settlements, the Fallout 4 mod we awarded Best Mod of 2017, was that it gave NPCs some agency in creating their own homes and shops on your settlements. All you'd have to do is zone an area for the type of building you wanted, and let your settlers handle the construction and furniture placement, which gave rise to cool randomized homes and shops that would improve and change while you were off doing other things.
Rise of the Commonwealth, the expansion to Sim Settlements, takes the idea a step further by letting NPCs not just build their own stuff but actually plan the settlement completely without your input. You can assign a city leader for each settlement, choosing from Fallout 4's NPCs companions, and put them in charge, as if making them mayor. They'll begin by scrapping the settlement, decide for themselves where zoned plots should be placed, and then set about building along with the other NPC settlers you've recruited. As the settlement grows, your mayor will even take into account the current shortcomings of the settlement, focusing on more farms or homes or shops depending on what's needed most. Rise of the Commonwealth is another way to have unique, constantly growing settlements without you having to spend time micromanaging everything.
Naturally, you can still contribute and build your own stuff if you like, but the idea is to feel like your settlers are capable of making decisions and managing themselves. They may even build over some of your own constructions (if you built something in their designated area) or even move items you've placed to more suitable locations. And why not? You've put them in charge, after all.
You can also help out by donating your spare junk to boost their scrap supplies, and since Sim Settlements gives you more time to explore you're bound to have tons of extra junk to contribute. You can also still set up supply chains to keep your settlements connected to one another.
As always, modder kinggath and his team have produced some informative orientation videos to explain the basic concepts and finer workings of the mod, and there are future plans to add a wider selection of NPCs that can act as city planners and even provide bonuses to the settlements they're assigned to. Sim Settlements, already great, just keeps getting better.