I have written and contributed to various open-source projects. Here is a selection.

Emacs Lisp

Sometimes during writing you recognize that it would be nice to change word order within a coordination: e.g., instead of “editing and revising” you may prefer “revising and editing.”  Placing the point on the conjunction and calling conjunct-mode will help you doing this “nice 'n easy.”

Place the cursor on the conjunction and activate conjunct-mode:

Adjust the extents of the left and right conjuncts as desired:

Transpose:

conjunct.el was developed by Cerstin Mahlow and me in the context of the LingURed project.  It works with Emacs and XEmacs.

Perl

Besides other Perl software, I have written several Perl modules, some of which are also available from CPAN.

Typesetting

My mpreport and mparticle LaTeX classes are surprisingly popular.

Malaga

Malaga is a software package developed by Björn Beutel for the development and application of grammars for natural languages.

I have written modules that allow you to work with Malaga grammars from Perl, Python, and Ruby programs. These modules greatly simplify the building of applications using linguistic knowledge.  My Malaga page has more information.

eduComponents

eduComponents is a suite of educational extension modules for the Plone open-source CMS. I have developed eduComponents together with Mario Amelung and Wolfram Fenske in the context of my doctoral thesis. The main goal of these components is to improve the effectiveness of face-to-face courses. The modules provide Web-based tools that support the creation, management, submission, and assessment of assignments and tests.

The eduComponents were nominated a Medida Prix 2009 Finalist, i.e., it was one of the top 10 projects among the 82 submitted projects.  The eduComponents are open-source software employed by many institutions around the world.  They are still actively maintained and developed at Otto von Guericke University Magdeburg.