TrailheaDX is the Salesforce developer conference. It was held in San Francisco on the 28th and 29th of June, in the Moscone West Center. The number of attendees has quadrupled from last year, with people coming from all around the world, as my colleague and myself traveled from Málaga (Spain).
This conference was born after the demands from Salesforce developers of having their own event. It is true that there is a zone at Dreamforce for developers, but that was not enough for us, and finally our demands were listened to and Salesforce created this amazing conference.
One thing to note about TrailheaDX is that the people giving the talks are product managers, directors or engineers working directly with the products, so you have first hand information.
There were more than 180 sessions to cover multiple and diverse topics. 3 key areas led the whole conference and were highlighted during the opening keynote with amazing demos run by Leah McGowen-Hare (Director of employee and Trailhead content strategy) and Sarah Joyce Franklin (SVP Dev Relations & DM Trailhead). The demos are already online, check this powerful demo of Einstein and this one about Salesforce DX both run by Leah McGowen-Hare, and also this one about Platform Events run by Sarah Franklin.