Libertarianism is the term for people who believe in the Non-aggression principle. (NAP)[1]
The NAP says "The initiation of force is immoral."
Thus libertarians believe that it is immoral to initiate force (against the innocent) though it is moral to defend yourself with force against its initiation.
Ragenwald rightly points out that the free software movement is more like going into competition with the company. Don't like the policies of a for profit (or even another open source) project? Build your own and compete.
The NAP makes it really easy to see the morality of various actions. Apple excluding software that is incompatible with the kind of store it wants to make: Moral. You might not like it, but it is not aggression.
The GPL restricting the way that software licensed under it is distributed or modified? Moral. You might not like it, but it is not aggression.
The workers taking over a company and kicking the owners and managers out to run it as a "workers collective": Immoral. Using force to take property from others violates the NAP.
Those same workers leaving to form your own auto company organized around your socialist ideals: Moral
The difference between libertarianism (those who agree with the NAP) and socialists, is that socialists do not agree with the NAP. This may sound like a tautology, but how many socialists oppose: (just to pick some topical examples.) -- Minimum wage laws -- Laws that require companies to recognize and negotiate with unions -- Universal healthcare -- Mandatory coverage terms for health insurance
All of the above require the use of violence (or its threat) to coerce people to act in a way that the socialists approve of.
Libertarians (by principle) oppose these positions because they violate the NAP. Socialists often support them. Also, practically, libertarians believe that all of the above make people worse off, increase poverty, etc. The NAP is the principle, but the philosophy involves recognizing the economic effects of violating the NAP are always worse than respecting it.
I've always seen the open source movement as intrinsically libertarian, and in a way, capitalist. If you don't like the terms of what's out there- compete. Getting others to contribute their time to make the product better is just an efficient form of competition. It works better for some types of software than others, but it is moral.
[1] Its popular these days, especially among those who came to call themselves "libertarians" because they like Ron Paul, to think it just means "freedom". But this isn't accurate. The founders of the Libertarian movement were clear, and the Libertarian Party required all members to sign a pledge to abide by the NAP as a condition of membership.