Plugins are otherwise referred to as extensions.
These are primarily used to improve the versatility of chrome.
You have to be descriptive to your questions, as there are numerous extensions used for a variety of purposes. However, below are a few extensions and their respective functions: 1.keywordeverywhere-it reports KW volume and 2.SEOQuake-it reports PA, DA and Back links to websites.
3.Wunderlist — Simply used for the to - do list.
There are many more, but be particular to what you need.