Seems to have the things KSP had when I first played it in 2013, before career was added

I’m surprised no one mentioned it yet, but Kitten Space Agency

It’s a free spiritual successor to Kerbal Space Program that tries to be everything that KSP2 wasn’t. It’s still in early development by its progressing fast and it already looks great and allows you to do a lot of cool things, and it’s also built using their own engine instead of Unity and has modding support.

And it’s not on steam.