Well I think your friend is asking the wrong question. He should be asking what would make me money, if Linux does that great. Now if your friend is like me, not a knowledgeable investor, I think he would be better off in a low cost mutual fund, vanguard has a bunch of cheap index funds to look at, www.vanguard.com . Vanguard also has a lot of educational reading available on it site about funds in general. If he likes reading books here is one on funds "Bogle on Mutual Funds: New Perspectives for the Intelligent Investor", ISBN 0440506824. And here is one on stocks "The Intelligent Investor", ISBN 0060155477. Intelligently investing in funds is MUCH less work then doing the same for stocks.
I wish him the best of luck, but if he has not done his home work he would probably be better off sticking it in a CD.
