Plugins to let user post from their blog

Hi all!

I’m using the Mesmerize theme. In your opinion, what is the best plug-in for a blog that will allow posts to happen from more than one unique user? For example, I’d like to display blogs from Ann and Tom intermingled by date. So if Tom posted on 5/1 and Ann posted on 5/1, I’d want that to display by date.

Also, is there anything that would “sort” different authors? Going back to Ann and Tom, is there a plug-in that would show all of Ann’s posts in one place and all of Tom’s posts in a different place?

Any guidance would be appreciated.

Thanks!