Provide all resources we have got.
Someone post all the prototype links here. I think everyone needs them for their reference. And Wireframes, if any, are necessary. If we can make a Concept Note like thing that will be great.
Because this is a big project so when we start making anything, everything should be taken care of. Many times it happens that we discuss something, come up with a great idea/feature and then forget it.
Now, let say, a third person asks me to explain the project idea to him, I won't be able to explain to him because I'm myself not clear about that.( For ex. the Discussion part). So if we know what exactly the future challenges will be,we would keep that in mind and write the code accordingly.
In short all, I think, we need is something like a documentation. :)