The pull-up is perhaps the most primal and useful of exercises. Have you ever tried to climb over a wall or fence, or leap onto a hanging fire escape when you've locked yourself out? Being able to do a pull up or two is the difference in these situations between a night in the cold, and your warm bed. Bring it on!
Join a team or create your own! There are lots of teams on Social Workout, and each gets its own page. A team can participate in
any challenge as long as at least one team member joins the challenge, and the challenge host adds the team to the challenge.