SugarCRM, the leading open source producer of Customer Relationship Management (CRM) software, have opened an office in Dublin to help to grow their presence in Europe:
SugarCRM expands into Europe - http://news.yahoo.com/s/infoworld/20070305/tc_infoworld/86528
I have always been a big fan of the SugarCRM product; I have worked on several versions of the application while customising it and extending it with custom modules, and I believe that technically it is brilliant and really shows that "enterprise" software is infinitely possible on the LAMP stack.
As always it is great to see another high-caliber software firm come to Dublin: I wish them luck!
Updated 2021 : note that the above post is out of date as it was originally published in 2007, but is left here for archival purposes. I have unlinked the external link as it is now dead.