The gems are only if you want to progress quicker down the research tree by “buying” the tech and unlock the structures faster.
But, it’s not required, you can progress normally by producing the required items and sending them to the research lab.
You can also earn “free” gems by watching an ad.
Once you have enough gems, you can plant a gem tree (that costs gems) that will produce unlimited gems albeit at a slower rate.
There’s a free game on iOS called Builderment.
It’s basically Factorio without the hostile mobs.
An automation game with unlimited resources so you can solely focus on optimization.
I have over 500 hours in my current world.
Totally playable, no purchases required.
The gems are only if you want to progress quicker down the research tree by “buying” the tech and unlock the structures faster. But, it’s not required, you can progress normally by producing the required items and sending them to the research lab.
You can also earn “free” gems by watching an ad. Once you have enough gems, you can plant a gem tree (that costs gems) that will produce unlimited gems albeit at a slower rate.