For those in the EU or otherwise able to take the opportunity to be at the event, FOSDEM remains one of the best European free software / Linux events and is completely free to attend. Among the keynotes for FOSDEM 2017 cover Kubernetes, software heritage, the complexity of copyleft defense, and using Linux in air traffic control. Main tracks cover architecture, building, cloud, documentation, and security/encryption. The event runs from 4 to 5 February in Brussels.
Where most of the technical discussions are at come down to FOSDEM developer rooms where there are dozens ranging from Guile to Mozilla to Valgrind to PHP to many other exciting topics. Though sadly no X.Org / Graphics Room, which used to be a big hit years ago.
If you have the opportunity to be at FOSDEM next weekend, visit FOSDEM.org to learn more about the event. While sadly I am unable to attend, I will certainly be going through all the video feeds and slide decks and provide any interesting remote coverage where possible.