Comment rules variants include 'area or territory' (Score 4, Informative) 57
Given the main article was paywalled, here's a summary of Go variations. Besides the minor stuff like 'where to put captured stones, cup or side', there's one fundamental difference: Whether to count area (count every stone towards score, aka Chinese counting) or territory (count empty points within your territory, aka Japanese counting).
This article is great, gives an overview plus specifics on 6 different rule sets in use: gomagic.org