SSH Agent is a graphical front-end to some of the OpenSSH
tools included with Mac OS X.
Specifically, it allows you to start an ssh-agent,
generate identities, and add identities to an agent. Additionally,
it allows you to make the ssh-agent global so that, e.g.,
it to do version control over SSH, and it has some functionality to set-up a secure tunnel. The source code
is also available.