Allowing anyone to post

I’ve got a specific situation where I’d like anyone to be able to create a new post – with or without registering.

I had a look at the role manager plugin but that doesn’t quite seem to make this happen. However it seems clear to me that WP isn’t far from my being able to do this somehow through role management.

Is there an easy way for me to accomplish this so that visitors to my site have the ability to create new posts? It’s possible I’m missing something simple :).

Thank you.