Mycelium is a free multiplayer strategy game that runs in your browser. You play a fungus spreading underground: grow into soil, fight your enemies for territory, and absorb them.
Its main rule is the supply line. Every part of your network must stay connected to your origin. If an enemy cuts through a thin strip of your territory, everything on the far side starts to wither and dies after a few seconds unless you reconnect it. Battles are won with chokepoints, encirclement and well-placed cuts.