Gentoo's emerge command is powerful, but it stops if you attempt to run it in the background, and it often takes a long time. Particularly when compiling stuff on a server, it's useful to have emerge work in the background even after I log out.

Solution: the screen utility. Before starting a long compile, I type screen, which opens a shell session that I can detach and reattach later. I start emerge, wait a little to make sure I typed the command correctly, then push Ctrl-A followed by D. At that point, I can log out while the screen session continues in the background. A few hours later, I type screen -x to reattach the session, often using a different computer than the one I used to start the emerge.

In general, the screen utility makes it easier to perform long running automated tasks, like compiling software, downloading large files, or converting media files.