Understand why it's free and where the offerer derives value.
- If it's from a company that is commoditizing its money-making products' internal dependencies, and it is in your interest for the software to become a commodity (e.g., you're pondering switching to Linux, which has patches from Google), great. Tough luck for those commercializing that software, though - so just make sure that development is sustainable.
- If it's from a company that's commoditizing its money-making products' complements (see https://www.joelonsoftware.com/2002/06/12/strategy-letter-v/ if you haven't), think carefully about how that complement relationship works. If it's Red Hat producing a window manager, sure, whatever. If it's Red Hat producing a complex infrastructure platform, and they make money based on support to make that platform work, maybe not so much.
- If it's from a company that's making money in an unclear, unrelated way (e.g., you're pondering using Android, which is developed by Google), look extremely skeptically and figure out what their real incentives are. There is a legitimate explanation for Android and Chrome: it's in Google's interest to promote the web as a platform, because they make money on web advertising. But that explanation might not be totally convincing to you, in which case running the other way is a fine answer.
- If it's from a source whose motivations are not linked to the capitalist machine (e.g., someone with a well-paying day job who's working on a side project on weekends), that's fine. Note that things from companies are almost never in this category.
- If it's from a company that hasn't yet realized that it's beholden to the capitalist machine (e.g., the early years of Ubuntu, or a young company with too much VC money), you might as well take advantage of it in the short term but have some plans about the long term.
- If it's from a source that you can pay, despite it being free, and you can afford to pay for it, do so. Pitch in to that developer's Patreon, buy the paid license for the neat monitoring product your company is using, etc.