Volkmar Kantor

The plugin provides the functionality to adjust the crop region of cropped images. It add buttons to the edit-pages and media-dialog to access a crop-editor. 
In the crop-editor you can choose one or more (if they have the same ratio) imagesizes and cut-off the part of the image you want.
The plugin is especially useful for theme developers who want to keep full control over cropped image sizes. If you want to dive even deeper, you can get informations about the hooks and filters on the <a href="https://github.com/vollyimnetz/crop-thumbnails" rel="nofollow ugc">github page of the plugin</a>.

Crop-Thumbnails

Amazing work on this plugin. It make developers and users life easier creating a handy-way to crop thumbnails in the used sizes across the site.

Where's the button "This plugin should be native"?

"Crop Thumbnails" made it easy to get exacly that specific image-detail you want to show in your featured image or gallery image.

Brianna Deleasa

This plugin allows you to upload a set of images via a settings page to be shown for posts without images. The images will be chosen at random on page load for any posts without a featured image (meaning each time the page is reloaded another random image will be chosen). Useful if your theme shows thumbnails for the posts, and you don’t want any posts without thumbnails.
UPDATE: Now you can select images specifically for certain post types as well as taxonomy terms.

WP Random Post Thumbnails

Allows you to select images to be shown at random for posts without a featured image.

Crop-Thumbnails vs WP Random Post Thumbnails