For servers I can recommend OpenBSD. Works as a charm with Zope, never had a problem. Very secure, very fast, dead easy to install. OpenBSD (and FreeBSD, I don't know?) have two types of packages for most software. Binary packages, that work like typical rpms, that is they have requirements on other packages and blablabla, and also source code packages, which are source code, makefiles and scripts to get stuff running on Open BSD. The good thing with the source packages is that you don't need new packages for new versions of OpenBSD, hence, these packages require less management effeort for maintainer, so there are more of them that are actually working. :-) I like OpenBSD, but my ventures into using it as a desktop wasn't very successful. But as a server it kicks both Linux and Microsoft ass. :-) If I has the time I would compare it with FreeBSD someday, it would be interesting.