A complicated history for this one, with the developer Rocket Jump Technology no longer existing as a business. The previous iteration of the game named King under the Mountain went open source back in January 2024, and now what was to be the big revamp is also open source.

Read the full article here: https://www.gamingonlinux.com/2025/04/colony-building-sim-mountaincore-is-now-free-to-play-and-open-source/