ssh-agent

Problem: a program I wanted to use (filezilla) did not understand the format of my ssh-key.

Solution: abstract away the authentication process from the program to ssh-agent.

Caveats: If the server only gives you one try to authenticate yourself, then make sure that the authenticating agent (ie. ssh-agent) first tries with the right key for this server. ssh-agent will try the keys in the order they were added to ssh-agent.