I am not sure if this goes into any category because Thrive is not finished and been in development for a long time.
It is free, volunteer made, open source, and looks like it has been getting updates for 5+ years.
This game is basically a fan-made Spore game. So far, they have developed only the cell stage.
But why am I mentioning it? Well, not many people know about it and since it is still in development, I thought I can at least spread a little awareness. But I mainly found this game because they are going to use Godot.
It’s free to download and play what they have done so far.