The reason I fell in love with scrumblr, is that it takes two seconds to get going with. You don’t need to register, sign up or log in. You just get started.
To check it out, just click here. You create a new board by simply using a unique URL - like http://srumblr.ca/your_team_name_your_board_name.
Now this tool may be lacking in functionality for more elaborate stuff, but it’s an excellent way to get you started.