Several years ago, I worked on a side project that required a lightweight operating system where I could run a simple C program and a UNIX shell, so I naturally gravitated toward FreeBSD, as opposed to Linux. The reason at the time (2004-2005) was that Linux distros like Redhat, Debian, CentOS, and even Slackware tended to need a lot of packages to support even a base installation (i.e. X Windows, GUI, etc., as well as the hundreds of seemingly required programs like perl and python, that we take for granted today).
Manuel Kasper has a great article at https://neon1.net/misc/minibsd.html which details how to slim down a FreeBSD instal to run on a small hardware form factor. In my specific use case, I used a Soekris net4801 running off of CompactFlash, with an Atheros wireless card, and the FreeBSD version I used was initially 4.11, then used 5.4.
There is now an entire project dedicated to this called miniBSD, and can be found at https://www.minibsd.org/. Depending on your needs, hardware requirements, open source licensing, etc., this could eb an ideal solution for your next project, whether you are building a specialized computing platform or some other specialized application or function.
