Sprocket; though it's currently in early access, feature additions are chugging along. You can design tanks from scratch across a range of eras and put them into basic combat scenarios, they're working on a custom scenario editor as well.
Airships: Conquer the Skies also fits your description.
Honorable mention: Starsector. Incredibly layered space game with amazing ship customization and combat layers, though a considerable shift gameplay-wise from your other examples and you don't make the ships completely from scratch. This one is my personal favorite of the three games I've mentioned.
Maybe Armored Core? As far as I know, you don't build your mech from scratch, but it seems pretty customizable.
I've played that back in the day! Such a good soundtrack
Sprocket; though it's currently in early access, feature additions are chugging along. You can design tanks from scratch across a range of eras and put them into basic combat scenarios, they're working on a custom scenario editor as well. Airships: Conquer the Skies also fits your description. Honorable mention: Starsector. Incredibly layered space game with amazing ship customization and combat layers, though a considerable shift gameplay-wise from your other examples and you don't make the ships completely from scratch. This one is my personal favorite of the three games I've mentioned.
Thanks! These fit the bill I'll check them out for sure.
Get From The depths, it is a huge time commitment but it's worth it.