INFURIATING Scott G. McNealy has never been easier. Just bring up math textbooks. Mr. McNealy, the fiery co-founder and former chief executive of Sun Microsystems, shuns basic math textbooks as bloated monstrosities: their price keeps rising while the core information inside of them stays the same. “Ten plus 10 has been 20 for a long time,” Mr. McNealy says. Early this year, Oracle, the database software maker, acquired Sun for $7.4 billion, leaving Mr. McNealy without a job. He has since decided to aim his energy and some money at Curriki, an online hub for free textbooks and other course...