The only drawback to this is app that to realize most of its potential (such as embedding SlideShare presentations on other websites or your blog) you really need a SlideShare account. But on the upside, the SlideShare LinkedIn app allows you to sign up without ever leaving LinkedIn. And it's free.

Polling

This one is created by LinkedIn. Much like the staple Question and Answer section of LinkedIn, the polling app allows you to query your connections about some burning question you might have.

The main difference is the Polling app returns rich looking charts with their answers. If you're just looking to poll your connections, then the free version of this app might work well for you.

If you're looking for more robust capabilities, like, say, polling large groups within the LinkedIn user base, each response will cost you US$50 (minimum).