WordPress Donation plugins allow the visitor to donate and allow you to accept online donations.
WordPress Sitemap Plugins allows you to create and add a Sitemap file to Google Webmaster Tools.
WordPress invoicing plugins allow you to create professional quotes and invoices that client can pay for online.
Landing Page plugins let you create a quick homepage for your website. Mostly this plugin allows you to create a website with easy drag and drops feature.
WordPress Restrict Content Plugins allow you to manage the access to your posts, pages and files.
WordPress related posts plugins display related posts in a sidebar or after posts as thumbnails, links, excerpts or full posts.