This book describes the implementation of a framework for easier development of extensions for the office software OpenOffice.org. Jexo was chosen as a memorable name and as an abbreviation for 'Java Extensions for OpenOffice.org'. The core theme is the description of the Jexo framework, the problems it aims to solve, and the functionalities it is supposed to offer. Through general discussions on framework development, it demonstrates how established patterns and concepts have been realized in the Jexo framework. Additionally, it takes a look at the structure, design, and usage of the Jexo framework. Finally, the strengths and weaknesses of the developed framework are critically examined, and a perspective on potential further developments and the future of the Jexo framework is provided.