I can remember first using MS Office 2000 way back in the day. The updates added into Office 2003 were phenomenal and really pushed the boundaries of desktop software. Microsoft Office 2007 incorporate even more changes which are now prominently found in Office 2010/2013. Developers who really love this software will create add-ins for unique custom features.
I have crawled Google and put together 25 promising add-ins supported by Microsoft Office 2010 & 2013. All of these add-ins are completely free to download and use forever. The Office software package includes so many great programs like Word, Outlook, Excel, and PowerPoint. Add-ins are meant to expand the default functionality while also improving your workflow.