rpc.pcnfsd daemon.
Unfortunately, most versions have a bunch of security holes. This
version of rpc.pcnfsd is ported to Linux and has like 40
security holes fixed. It supports shadow password files.
I am afraid there are still some holes left in the code but this version should be much safer to use than any other (in particular, all Theo's fixes are ported here, too).
I would like to advise you to use in in conjunction with Wietse Venema's portmapper, rather than any other portmap program.
This program is not maintained as I don't run any Linux (or other) machines with PC-NFS any longer.
Download: pcnfsd.tar.gz.