Its a Spawner. U put the Spawnpoint with MCEdit over the middle of the spawner so they spawn on that give a signal through the tripwire and to the commandblocks. there it is different u can change the gamemode oder the spawnpoint oder the gamrules or somethin like this it also was used for a lot of PvP and Adventure Maps :)
Had a few issues pasting it but once the server came back it looked amazing. I had to //drain the bottom room and find the water leak. Also the beacon in the middle had to have a clear view of the sky to activate up through the tree at the top. Once that was all working it looks amazing with the beacon going up thru all the levels. Truly amazing work.