A couple of years ago I ran two free Lucene Hackdays in London and Boston (the latter just before Lucene Revolution). Here's what we got up to with the kind support of Alfresco, Bloomberg, BA Insight and Lucidworks http://www.flax.co.uk/blog/2016/10/21/tale-two-cities-two-lucene-hackdays/
I'd like to do this again during the weeks of 8th and 15th October in London and Montreal (so just before the Activate event). It's a great chance to get together IRL with other Lucene/Solr/Elasticsearch hackers! I have a venue for London but a sponsor for evening curry/drinks would be wonderful, and for Montreal I still need a venue and evening sponsor - do let me know if you or your employer can help.
I'll post again once there are more details and with a call for ideas as to what we should work on.