The game has a robust Steam Workshop community. Many complex mods, total conversions, or custom blueprints are shared in compressed archives.
Seeing the game mentioned as a .rar file usually implies a few specific contexts: Medieval-Engineers.rar
It is worth noting that Keen Software House officially ended active development on Medieval Engineers in 2020 to focus on other projects. However, the community remains active through the program, where players continue to patch the game and add features, ensuring that even a "legacy" file like a .rar backup remains playable and relevant today. The game has a robust Steam Workshop community