Guess what Steven A. Ballmer has been up to for the last several years. (No, not just cheering for the basketball team he owns, the Los Angeles Clippers.) It’s a novel project, and he plans to take the wrapping off it Tuesday.

But first the back story, which is a valuable prelude to a description of the project itself.

When Mr. Ballmer retired as chief executive of Microsoft in 2014, he was only 57 and quickly realized “I don’t, quote, ‘have anything to do.’”

As he looked for a new endeavor — before he decided to buy the Clippers — his wife, Connie, encouraged him to help with some of her philanthropic efforts, an idea he initially rejected.

“But…