Any non-excludable goods, which includes public goods (which are also non-rivalrous) are very difficult to profit from. These include lighthouses, laws, national defense, clean air and water, a sustainable population of fish and game, and so forth.<p>I say "very difficult" because search engines, for example, are non-rivalrous and non-excludable in practice. They are "public goods". The trick is, access to the attentions of and data generated by search engine users <i>is</i> excludable, and this is the good that Google actually sells. But any sort of non-excludable good from which your consumers cannot generate an excludable good you can sell for others would be unprofitable.<p>Programming languages (mentioned by another post) are another good example of a public good: they are non-rivalrous, and while they may be excludable as long as you sell the only compiler/interpreter/runtime and sue everyone else who writes a different compiler/interpreter/runtime, in practice no one will pay for a programming language anymore so you have to make it non-excludable for it to even exist in the outside world. Likewise, Google is probably excludable in the sense that they can set up a paywall before you use it, but in practice Google has chosen to make the search engine non-excludable and it's hard to see how a paywalled search engine would work (though I won't rule it out as a possibility).