This event is hosted in Trackmania and in the title(s) Trackmania² MultiEnvi. You can participate on your own and registration is not required. You need to have the title pack Trackmania² by Dommy installed. And there is a map pool that you can contribute to.
This event is played in the Trackmania² Titlepack by Dommy. Players need to own all four TrackMania 2 games in order to play.
The Mania Exchange Knockout is an online competition where the last player to finish each map is knocked out until the winner remains. You can read the full rules here and a more detailed explanation of how the competition works.