OpenCiv1 is an ambitious open source project that aims to recreate the classic 1991 Civilization 1 game designed by Sid Meier and Bruce Shelley. The project, hosted on GitHub, represents a complete rewrite of the original game's code while maintaining its core gameplay mechanics and visual style. The project uses C# rather than the original C and x86 assembly to ensure platform independence and modern compatibility.

Unlike simple emulation, OpenCiv1 replaces the original game's copyrighted code with new implementations that perform identical functions but under the MIT license. The project requires users to own a legitimate copy of the original DOS Civilization game, as it doesn't include any of the original game's files. Virtual CPU emulation handles some assembly code while the rest has been rewritten from scratch. The developers plan to replace all copyrighted resources including graphics, music, and text with copyright-free alternatives before final release.

The project welcomes contributions through multiple channels including testing, code translation from pseudo-assembly to C#, and creating visual and audio themes. The developers emphasize that while the source code differs significantly from the original, the goal is to preserve all original rules, functionality, and the classic game's appearance and feel. The project is currently in active development with both first-stage code rewriting and second-stage modernization milestones planned.