FOSDEM is the largest European conference on Free and Open Source software, organised next year on 2&3 februari in Brussels, Belgium.
For the past years, I've organised a geospatial devroom  there together with a team of other people. In the past OSM and OSGeo have also had a booth at the event.
I believe it is one of the most interesting events one can attend in Europe - both on a technical level and to learn from other communities (eg there usually also is a community track ). It also gives the opportunity to people outside the geospatial world to learn about our solutions.
I have decided that I will not be taking the lead for organising a track this year (I will be involved in organising the conference itself), but I hope some other people will pick this up. Note that the work one needs to do is spread and promote a call for presentations and make a selection of the speakers. FOSDEM itself is taking care of the venue, so one does not need to be from Belgium to organise, though of course you should be present during the event.
The call for devrooms  is closing this Thursday. If people are interested in organising (or helping organising) the devroom - I can send you the proposal of last year. Also note that every year the number of requests for devrooms is much larger than the supply - writing a proposal does not guarantee a space.