Niconico douga (ニコニコ動画)
webpage:
http://www.nicovideo.jp/
Niconico is a Japanese onomatopoeia for smiling.
Douga is Japanese for video.
Add them together, and it means video that makes you smile.
That is exactly what happens when you join and start viewing videos that are uploaded onto niconico douga.
The concept is simple that is similar to
youtube; one can upload and view hilarious videos made by amateurs. Of course, the other gray-area use is being able to view the latest anime MINUTES after it was aired (obviously with no subtitles).
But niconico takes a step further than youtube in which it allows members to start adding comments to the uploaded video itself. The English wikipedia sums it up as "youtube meets Mystery Science Theater 3000." This gives an added plus of indirectly watching the video amongst others while laughing at some of the funny comments that they made at a certain scene. Of course, you have the option of disabling the comment feature so you can watch the video without seeing massive texts scrolling through the screen.
Here's a sample screenshot of niconico:
Title: I let my friend play the
Super Mario World that I created Version II. (自作の改造マリオを友人にプレイさせる 第二作)
As you can see, people are commenting on how Mario died by falling into the lava by accidentally hitting the hidden block. The kanji word koumei (孔明) is a slang that the viewers made for those articulately placed hidden blocks which leads to Mario's death. The wwwwws is similar to LOLOLOL.
Unfortunately, there is no English version of this highly popular online video-sharing site, so you need to have a good understanding of Japanese to join.