[jackklika]

Mindustry[1] is an open source game that works perfect on mobile, especially if you have a big screen. You can find it on app stores or download it manually.

It's like factorio but more tower-defense and round-based. Much more approachable while still being really fun.

[1] https://github.com/Anuken/Mindustry

[MayeulC]

Oh, in the open-source department, there's also Unciv which I'm keeping an eye on. It could be improved, but it's quite fun already. It's a civilization clone.

https://github.com/yairm210/Unciv

[IggleSniggle]

This game destroyed me. It works well even if you don't have a big screen (relatively speaking anyway. I played it on an iPhone 7. You can't really get screens smaller than 4.7 anymore).

[k__]

Factorio was a bit too much for me, but I'll look into Mindustry, thanks!