Zotero's open source-ness has created a pretty rich ecosystem of applications and tools that work with it. Here are a few, and you can find more on the Zotero Plug-ins page
I'll be adding more to this - I'm trying to make a series of shortish (around 20 minutes) screencasts that demonstrate Zotero.
As a open source tool, Zotero has a robust number of third-party add-ons (plug-ins) that really make it even more useful. You can find a (not comprehensive?) list on Zotero's Documentation Page.
I have started some demo videos for these below.
Here are some additional videos (some I created, some from Zotero's documentation, that may be of use).
12/22/17: This was created as an aid for two webinars I did for WSU's Global Campus. (Links below). It was before Zotero's big 5.x update, so this will be slightly out of date, although mostly still usable.