Starting off as nothing but a tiny little cell in a massive world, Thrive is a free and open source evolution sim backed up by the power of science.
Quite early on in development still overall, it is however very playable already and you can have a little fun exploring and eating away at various resources to evolve your creature. It's like a much more detailed version of EA's Spore (in the early game stage). Now powered by Godot Engine, their progress on it seems to be speeding up.
Thrive 0.5.3 is up now and it brings with it numerous improvements to the flow of things like key rebinds, translation support, a process panel to show running processes in your cell, big improvements to the save game system, you can pan the camera in the editor now, music fade improvements, tips on the loading screen, plus lots of bug fixes to make it a lot smoother.
Check out their latest release trailer:
Work is already well underway for the next version, which will have a fancy new binding agents feature which wasn't quite ready for this version. Once that's ready, the next release will go up with that and whatever else they've done. They're also working on thermoplasts, 3D stages and absolutely loads more that sounds exciting for an evolution sim.
You can follow it on the official site and GitHub. It's free and open source. They also take donations to their Patreon, where if they manage to hit an additional £100 per month one of their team will be able to actually work dedicated part-time on it which would be great to see hit.