Extensions for NeoOffice, Libreoffice, EuroOffice, Apache OpenOffice, and AndrOffice.

AndrOffice offers 3 extensions.

 
Apache Open Office claims the following number of extensions:

By operating system:

• 752 extensions for Windows;
• 684 extensions for Mac OS X;
• 704 extensions for Linux;
• 668 extensions  for Linux x86_64;
• 657 extensions for Solaris x86;
• 655 extensions for SolarisSparc;

By component:

• 391 extensions for the program as a whole;
• 284 extensions for Writer; 
• 195 extensions for Calc;
• 100 extensions for Draw;
• 84 extensions for Draw;
• 29 extensions for Base;
• 13 extensions for Charts;
• 10 extensions for Math;

Doing a keyword search, there are:

• 159 extensions which are dictionaries;
• 51 extensions which are templates;
• 34 extensions which consist of clipart;

EuroOffice offers 17 extensions.

LibreOffice claims:

• 304 projects with 680 available releases.

NeoOffice does not appear to offer any extensions.

These numbers were initially compiled on 21 December 2016. 
The most recent  update was on 30 December 2016.
Not all figures were verified when the most recent update was done.