screenenv is a simple gadget to be used together with GNU Screen. It will make applications running within screen see some environment variables from the currently active screen client, not based on the first attached screen client. This enables applications to use the appropriate X display, SSH agent forwarding settings, etc.

Consider the situation: You have a screen session, originally started on a local desktop; later, you attach it over ssh as well (with X forwarding enabled). Now you do your happy mutt mail-reading, but stumble over an image attachment. If you try to open it over ssh, the picture will show up on your local display, not the ssh-forwarded one.

But if you preload screenenv, applications trying to use X will automatically choose the appropriate $DISPLAY based on the session with the least idle time!