My favorite tool for capturing EA modeling is Essential Architect Manager. View this tool at http://www.enterprise-architecture.org/ See rmtoo which is an open source requirements management tool at http://www.flonatel.de/projekte/rmtoo/. The last update was in 2012 but the source code is available which means you could potentially make updates yourself. Trak an enhanced wiki and issue tracking system for software development projects which can be viewed at http://trac.edgewall.org/.Another tool is Archimate Modeling at http://archi.cetis.ac.uk/ however that is more UML. I hope this is off assistance.

In addition to the tools mentioned by Maurice Dawson, have a look at the requirements tools subsection on the Tigris.org website: http://requirements.tigris.org. If you would consider a not open source tool, I highly recommend an appropriate edition of Enterprise Architect (http://www.sparxsystems.com). Their products are considered the best in class. Considering the comprehensive set of features, they are very modestly priced, especially academic licenses.

Dear Dario (and others),

I realize it has been a long time since the last contribution to this question. One Linux compatible requirements management software that I have seen before is from Polarion - please see the two links below. And it would be interesting to hear whether you have already made a decision regarding your question, and (if so) which software you picked. Thanks, 

Emre 

Dr. Emre Erturk 

http://www.polarion.com/products/requirements/benefits.php

http://www.polarion.com/downloads/requirements.php

In the end I did the requirements analysis by myself without the use of any software.