In this arena, you start with a handful of units and a small base (marines and a bunker, by default). Everything you kill respawns as yours from your base. Gather reinforcements with your troops, defend your base at all costs, and destroy all opponents to win.
Americas: battlenet:://starcraft/map/1/311293
Europe: battlenet:://starcraft/map/2/218947
Asia: battlenet:://starcraft/map/3/133724
Recycle Arena offers many standard features, including AI players, custom teams, and observers (so you can do things like 3v9 AI, though the AI is not super challenging).