#1: Wolfram Alpha
Summary: This extension allows you to query Wolfram Alpha from any webpage. Wolfram Alpha isn't a search engine, it is referred to as a computational knowledge engine. When you conduct a query via a search engine you often have to put each entry in separately to get accurate data. With Wolfram Alpha you can put all of it in as once. For example, if you are searching for data on different planets, Wolfram Alpha might be a better solution. If you want to find the answer to a complex mathematical equation, Wolfram Alpha would also be a better solution. If you subscribe to the pro version it will show you all the steps to reach that solution.
Summary: It allows you to shorten the current URL, gives you the same shortened URL every time you use the extension on the same page. I usually use goo.gl for my shortened URLs, but sometime I get an error message when using that extension, so this one my fall back.
#3: Shareaholic for Google Chrome
Summary: An easy way to share & bookmark great content from anywhere on the web with Facebook, Twitter, Pinterest & 200+ other services. You can also get a shortened URL for the webpage as well as access your sharing history.
#4: To Do List
Summary: Create a simple to do list from any open tab/window. Drag and drop the items to order the list. There is not advanced about this extension. If you are looking for a simple way to stay on top of tasks this extension might be what you need. The number of tasks to complete show up on the extension as a daily reminder.