PinDax, is a new site I learned about from Larry Ferlazzo's blog. This is a place where a user can create messages boards to collaborate w/ their users. It is very similar to Wall Wisher in that respect and has some very nice features to make it an attractive option for users.
PD is great at giving people the option to create embeddable "sticky notes" on their site. From there you can have users add comments, join a chat, organize by layers, etc etc. There are some really cool things that a user can do.
The one area of PD that I was not so fond of is w/ all the nice options you have it's not as user friendly as Wall Wisher. WW being more mundane actually simplifies itself for their users which turns out to be a plus. I think if PD didn't have so many links to click or items to choose from it might make the user experience a bit easier.
Give PinDax a try by clicking here.