Mike McQuaid shared some background on the approaches they’ve taken (and their pros and cons) to make Homebrew financially sustainable.

For predictable donations we set up the standard (at the time at least): a Patreon account. We offered nothing in exchange for donations but to told people we were an entirely volunteer-run project.

… We show users a one-time message on first install or on a Homebrew update to tell them we needed donations and where and how to do so. As soon as this message rolled out we saw a huge jump on donations eventually settling between $2500-$3000 a month on Patreon…