Jetpack - Jetpack offers SEO and security plugins for Wordpress.
Typeform - Create beautiful, next-generation online forms with Typeform, the form & survey builder that makes asking questions easy & human on any device. Try it FREE!
WP User Manager - The most customizable profiles, community builder and membership WordPress plugin
Survey Monkey - Create and publish online surveys in minutes, and view results graphically and in real time. SurveyMonkey provides free online questionnaire and survey software.
UpStream Plugin - UpStream Plugin is a free-to-use project management plugin that allows you to manage various types of projects right from your WordPress site.
Google Forms - Simple web forms from Google.