Many Implementations
There are many different programs that perform the same functionality as the original OpenSSH ssh-agent, some with very different user interfaces. PuTTY, for example, uses a Graphical User Interface in its bundled Pageant ssh-agent.
There are tools designed to provide key-agent functionality for both symmetric and asymmetric keys; these usually provide ssh-agent functionality as one of their application interfaces. Examples include GNOME Keyring and KWallet.
Some monolithic SSH clients include the ability to remember SSH passphrases across sessions. Examples include: SecureCRT.
Read more about this topic: Ssh-agent