Jason's 18xx Rules Template and Style Guide
Jason's 18xx Rules Template and Style Guide (The RTSG) is a resource for anyone writing or editing rules for 18xx-style board games. It is broken into three sections:
The RTSG itself includes a much more comprehensive introduction and guide to use. It is a living document that is updated when I have time / feel like it / see a need to do so. It currently exists as a Google Doc.