Shishi is a (still incomplete) implementation of
Kerberos 5, which can be used to authenticate
users in distributed systems. It contains a
library that can be used by application
developers, and a command line utility for users.
Shishi supports Kerberos authenticated telnet
client/server, IMAP client/server (via GSSAPI),
SSH client/server (via GSSAPI), rsh/rlogin client,
and a PAM module for host security.