Razesdark

This plugin will allow all authors to have their own tweets shown on in the widget area of their posts, by adding it to their profiles. 
That way any multi-author blog can let their bloggers promote their own twitter account and not a joint account.

Author Based Twitter Widget

A Author based twitter widget, made to help multi author blogs have individual twitter widgets for their authors.

flocsy

Authors Widget shows the list or cloud of the authors, with the number of posts, link to RSS feed next to their name, avatar. It is useful in a multi-author blog, where you want to have the list in the sidemenu. 
The widget can also display an “Author Cloud” if <a href="https://wordpress.org/extend/plugins/seo-tag-cloud/" rel="ugc">SEO Tag Cloud plugin</a> is installed.

Authors Widget

Authors Widget shows the list or cloud of the authors in the sidemenu.

Author Based Twitter Widget vs Authors Widget