In January I discovered Bo Haglund's double dummy solver, called DDS. I had been looking for an open source solver running on Linux ever since I started playing Bridge, so this was a very nice finding. It is very fast and the API is nicely documented.
Of course, there are Debian packages, one for the (static) library (libdds-dev), for the ddd driver frontend (renamed to dds as there's already some other package called ddd), and for the python extension (python-pydds).
I am working on a GTK2 frontend called tenace. So far it features a basic hand editor, can play cards, and compute double dummy/par scores. The .lin import/export is not yet complete, but basically works.