The foundation is involved in digital money but unlike Bitcoin it would not be anonymous digital money. In Kenya M-pesa is being used for almost half of all transactions. Digital money has low transaction costs which is great for the poor because they need to do financial transactions with small amounts of money. Over the next 5 years I think digital money will catch on in India and parts of Africa and help the poorest a lot. (http://www.impatientoptimists.org/posts/2011/01/mobile-phones-savings-a-powerful-pair)
Bill Gates was asked about cryptocurrencies on a Reddit AMA. He seems to know it quite well, but is involved in something different: M-Pesa. More of a payment solution and alternative money, but similar use case.