If you are attending Cannes lions, make sue to prep your smartphone with Campaigns Festival app, which helps you keep track of the must-see seminars and meetups you want to catch.
When the sun goes down (but it's always five o'clock somewhere, especially in Cannes) use CreativeBrief's hilarious Gutterbarometer - the app which keeps tracks of your trips to the Gutter bar. If you dare! Created by CreativeSocial and Dare. Fun stuff.
Another one: Cannes Centrale, a "mobile conversation platform for the lions".
* updated to add more linkage!