Have you ever felt great hatred towards some person? Was it as if you can visit hell for eternity to punish him? The rumor tells of a site, opened only at midnight, called the Jigoku Tsushin. You can write the name of your grudge there and that person will be sent to hell by the Jigoku Shoujo. This rumor is apparently true.
Both series are adaptations of a manga that was made into an animated series as well. It needs to be said that neither of these was an expensive drama, so don't expect to find astonishing special effects.
Both talk about death, but more specifically about the person or entity who accompanies humans to the afterlife. Theses characters' reasons for doing so are quite different though.
Even though there's some kind of overall plot with the main characters, usually each episode is focused on an independent case. That makes these series easy to watch, since you can watch each episode individually.