Some people care a lot about Open Source Ideology. The BSDs are free in a different way than Linux is Free, GPL vs BSD licensing. Separately the source code fo

Some people care a lot about Open Source Ideology. The BSDs are free in a different way than Linux is Free, GPL vs BSD licensing. Separately the source code for FreeBSD is pretty clean and easy to read. I needed to modify the behaviour of one of the core utils a few years ago, and I found it very easy to do. The C library that it uses is also pretty well written. It won't be quite as clean as OpenBSD, but it is a lot simpler than trying to figure out glibc(which was possibly intentionally obfuscated to avoid lawsuits). The build system for FreeBSD is also pretty simple to figure out. You can download the source, modify the kernel or userland and rebuild world in like at most like 30 commands. I haven't tried with Debian or any Linux distro, but I would imagine it would be harder given the separation of the kernel and userland.