Lightweight Contact Form
Lightweight Contact Form is claimed by is authors to be the lightest contact form for WordPress. This plugin is designed for the fastest pagespeed. So, there is no settings page, no CSS stylesheet, and no extra files.
If all you need is a simple contact form to take messages from site visitors, and fast page speed is your priority, this minimal contact form is for you.
Although this form is lightweight and simple, it blocks Spam, and has both client-side and server-side validation.
FluentChat – Live Chat for WordPress
FluentChat is a dedicated WordPress plugin offering a free live chat option for your website.
You can have unlimited operators, unlimited messages, unlimited live chats, and unlimited archives.
You can view all the chat archives in the back-end and let visitors receive the chat logs in their inbox. This option can be disabled on the settings page.
When none of your operators are logged in, you can show a contact form, asking their Name, Email, and Comment.
WG Plagiarism Checker Pro
Check plagiarism of your wordpress post with the click of a button. So when people add content to your site you can check if it has be used elsewhere and check to see if you are breaching copyright.
The first 50 checks are free, then you need to pay with prices starting US$5 for 1000 queries.