This story was originally published by ProPublica. ProPublica is a Pulitzer Prize-winning investigative newsroom. Sign up for The Big Story newsletter to receive stories like this one in your inbox. Last June, drawing on the largest trove of confidential American tax data that’s ever been obtained, ProPublica launched a series of stories documenting the key ways the ultrawealthy avoid taxes, strategies that are largely unavailable to most taxpayers. To mark the first anniversary of the launch, we decided to assemble a quick summary of the techniques — all of which can generate tax savings on a massive scale — revealed…