A YouTube video usually gets credited to whoever has uploaded it, but if your video involves anything more than speaking into a webcam, other people are likely to have been involved. I'm In That! aims to give credit where credit is due, letting anyone who appeared in or worked on a YouTube video identify their role.
The site describes itself as "like the IMDB but for YouTube", and that pretty much covers it. Set up an account and add your videos, then invite others to describe what they did on them. Given YouTube's content is dominated by music clips, I'm not sure how widespread this will become, but it beats trying to list everyone in the video description.