FOSDEM (Free and Open source Software Developers' European Meeting) is a free event centered around free and open source software development and it is recognized as the best event of it's kind in Europe. The event is organized by community for community and is free of charge.
This year are expected 6000 hackers to participate at 400 lectures in 2 days.
It will take place on the first weekend of February (2-3 February) on Brusseles (as usual).
Here is the schedule: https://fosdem.org/2013/schedule/