Microsoft : Enterprise Softwares, Operating Systems, Software Infrastructure
Billgates currently own only 100 million shares in Microsoft which is nearly 1.6% as on March 2020. He had significant investments in other companies through Cascade Investment.
Other than Microsoft shares, his wealth is mainly through investments in Berkshire Hathway, Waste Management, Canadian National Railway, Caterpillar, Walmart, Ecolab, Crown Castle, FedEx, UPS, Coca-Cola Femsa SAB.
He and his wife donated more than 45 Billion USD as part of charity. Actually if Bill Gates had not donated money to charity institutes, he would have been World Richest Billionaire. He loved to give part of his wealth to charity institutes rather than having a crown of World Richest Billionaire.
Bill Gates and Warren Buffet had given good amount of their wealth to charity institutes.