Vinod Khosla, the billionaire venture capitalist and co-founder of Sun Microsystems, was already among the world’s richest men when he invested a few years ago in SKS Microfinance, a lender to poor women in India. But the roaring success of SKS’s recent initial public stock offering in Mumbai has made him richer by about $117 million — money he says he plans to plow back into other ventures that aim to fight poverty while also trying to turn a profit...Mr. Khosla plans to start a venture capital fund to invest in companies that focus on the poor in India, Africa and elsewhere by providing services like health, energy and education...[He] wants to show that commercial entities can better help people in poverty than most nonprofit charitable organizations...Some nonprofit experts say commercial social enterprises have significant limitations and pose conflicts of interest. But proponents like Mr. Khosla draw inspiration from the astounding global growth of microfinance...