Despite using FreeBSD I had the same question as I had never really touched them. From reading up on it, it looks like they're old remote versions of various commands for interacting with a server/mainframe from a thin client. For example, rcp copies to a remote host, rlogin starts a terminal session on a remote host, etc.

I could well be missing nuance though. My experience with FreeBSD is using it for my server for ZFS' gloriousness.