This extension allows one to use the open source R statistics package within OpenOffice Calc. It comes with a number of features, including new user interface windows for using advanced statistical tools, new spreadsheet functions, and a way to use R scripts within Calc.

ConvertTextToNumber replaces numbers and dates, formatted as text, with real numbers.
Choices can be made about marking of cells, including cells with non- default decimal separators, conversion of dates, and more.

As a result of the conversion, the text cells will become real numbers, and then will be counted in formulas Calc.

Classic data processing applications for spreadsheet users: rows of an update spreadsheet are matched by keys with a master table and change master rows. Cell properties, row and column formulas are preserved. Update operations are controlled by various specifications in a spreadsheet. The design enables a well organized, rolling operation: master generations, checkpoints, reruns, audit trails, check balances.
new: implemented as ADD-On:

This is a template for grading a rather complex setup of course work.
It is intended for instructors to keep track of their students' performance
without having to use calculators etc.

In this template, the following are accounted for
4 midterms
2 assignments
attendance

For midterms:

EuroOffice Dictionary is a dictionary toolbar. This toolbar continuously displays translations for the word under the cursor in a text document and provides other useful features. The professional version includes more dictionaries, supports more formats and has more features than the free version.

EuroOffice Solver Professional provides 4 fast algorithms to solve optimization problems in OpenOffice.org Calc.

Provides integration with clker.com online clipart to openoffice.org. Simply, the cliparts you choose and save to your clipart basket, will appear in the extension window inside openoffice.org. Better, we have almost all cliparts in ODG format, SVG and PNG so you don't have to worry about compatibility issues.

A library of Calc functions.
Functions
This version adds only the SQLREQUEST function to Calc.
SQLREQUEST allows to query a JDBC data source. It is similar to the SQL.REQUEST function provided with MS-Excel.

The Creative Commons Licensing extension provides the ability to select and embed a Creative Commons license in Writer, Calc and Impress documents. In addition to embedding the license in the document metadata it provides a visible notice in your document.

This extension convert recursivly Microsoft Publisher document in OOo format (impress)

...but this not the perfect converter : I don't parse the pub file : I just use Publisher COM component.
So Publisher has to be installed !
Anyway, I think it can be usefull for a lot of people "captive" of Publisher.