MacKenzie Scott, the billionaire philanthropist known for her impromptu multi-billion dollar donations to charities and racial equity causes, announced Tuesday that she has given $2.7 billion to 286 organizations. It is the third round of major philanthropic gifts Scott has made, which together rival the charitable contributions made by the largest foundations. Scott, the ex-wife of Amazon founder Jeff Bezos, wrote in a Medium post that she and her husband, Dan Jewett, made the donations to enable the recipients to continue their work and as a “signal of trust and encouragement” to them and others. And she made clear in her announcement that she is troubled by the increasing concentration of vast wealth among a small proportion of individuals. She and Jewett worked with a team of researchers and philanthropy advisors “to give away a fortune that was enabled by systems in need of change.” “In this effort,” she said, …