Well pretty much everything if you ask the plan9 guys. ;) Over the years a lot of the Linux system infrastructure has been reworked: /dev --> udev SysV init

Well pretty much everything if you ask the plan9 guys. ;) Over the years a lot of the Linux system infrastructure has been reworked: /dev --> udev SysV init --> systemd/upstart su/sudo --> policykit (for desktop stuff) sockets/shmem for IPC --> dbus (IPC for desktop apps) xorg --> wayland (not quite yet) I personally think cron and atd need to be updated and combined and possibly integrated with init. If you're not running a server and instead are using Linux for a desktop or laptop then nearly all these daemons could be reconsidered as well. Of course, sometimes you might decide that known deficiencies are better than unknown deficiencies or that simplicity and familiarity means the old tools are still preferred. FreeBSD is pretty old school and very functional after all. But there is plenty of room for experimentation.