This is NetHack Summer tournament. It runs from July 17th midnight at UTC midnight (running through all of 17th) and ends at August 14th (also running through all of 14th).
NetHack is a classic roguelike game. If you don't what that is, try using a Google search.
You can check out tournament rules from the rules page.
There is a list of available trophies and competitions on the trophies page.
This tournament utilizes existing public NetHack servers, such as nethack.alt.org. There are servers in both sides of the Atlantic for low latencies. People not living in Europe or Americas may find it harder to find a low latency server.
The official place of contact with the Junethack developers is at the #junethack IRC channel on Freenode. We also read RGRN and the NAO forum.