Naively, some Objectivists may come to believe that working on open-source software is, while perfectly constitutional, not a good action to take. "You work on software that the masses could use, and instead of selling it and earning a honest buck, you give it away to everybody, and have others benefit from your efforts. What's in it for you?" But let's first formulate a definition of what is beneficial and what isn't.
Again, I will extract a suitable definition out of the Neo-Tech text:
"The meaning of moral in Neo-Tech is simple and direct: Whatever is consciously done to help fill human biological needs is good and moral (e.g., the productive actions of honest people). Whatever is consciously done to harm or prevent the filling of human biological needs is bad and immoral (e.g., the destructive actions of mystics and neocheaters)."
"moral" here is "beneficial" in our terminology. The validity of this definition is also evident. So how Open-Source measures against it? Very well, actually. Open source software was so far used by millions of users worldwide, greatly facilitated some of the jobs they had to do with their computer, and generally contributed to everyone's well-being. The very action of creating a useful software for everyone to use is beneficial as it eventually can help fill human biological needs.
Now, some hardcore Objectivists can ask "But what about your own self- interest?". Self-interest here is relevant, but in subversive ways. The open-source developer does not economically benefit from the software he wrote, as much as he would, had he sold it commercially (and assuming it would indeed become successful). However, he does benefit, from having more potential users and co-developers, from making sure his software or one of similar vestiges will remain available as time goes by, and from a boost of happiness knowing that people are using your software.
Usually, getting a non-free piece of software to become successful would take a lot of effort on the developer's part, and you always risk a player with better resources competing with you. While it is itself beneficial as well, it may not yield the same immediate and long-term profit from working on an open-source package.