while no port in openbsd that can just make .torrent file this port can be useful with net/btpd or similar light-weight bittorrent protocol daemon.
http://www.rootshell.be/~mitya/ports/createtorrent.tar.gz pkg/DESCR: CreateTorrent is a small and fast command line utility for all Linux and Unix operating systems to create BitTorrent files easily. BitTorrent files can be created from either one file or a collection of files that are grouped together into a directory.