As is typical of so many families around Christmas, we have been playing a lot of Monopoly. It seems a lot of people use a number of house rules (and many people have been using them for so long, that they are not even aware that theu are not following the standard rules.
I have a good understanding of the standard rules and the tournament rules and clarifications that have applied over the years.
As a family, we have over time adopted a number of particular variants that we enjoy. So much so that I have a page of our rules.
Our favorite variants are Travelling Railroads (which let you travel between the owners and your own train stations) and Six Railways (which turns the two Utilities into additional train stations).