Game engine used?

What game engine are you using?  Also, what language are you using?

The game engine is LibGDX and the language is java

Eight months ago I chose Unity and C#. C# because of college courses in the mid 90s. Unity because of how they licensed it. libGDX might have been a better choice. Now I am so far in the project Unity and C# is beginning to produce.

When Space Haven comes out of early access, will it be open for modding?

Space Haven can already be modded, although it is not that easy. We do have modders discussing it on our Discord server:
https://discord.gg/zx2AN4F

Unity is good. We just started with LibGDX 8 years ago and stuck with it so that's why we're using it. =)

thank you