Best free "tower defense" games

GAME GENRE – Tower defense games are built around a wonderfully simple idea: enemies are coming, you have a base to protect, and apparently the best solution is to build a lot of towers and hope for the best. Players place defensive structures along predetermined enemy paths, choosing where to build and which weapons or abilities to upgrade. As waves become stronger, strategy becomes increasingly important: a tower in the wrong position can be about as useful as a cardboard umbrella in a storm. Different towers may specialize in slowing, damaging, or weakening enemies, forcing players to balance firepower, range, cost, and timing. Some games keep things simple with a fixed screen and clearly defined paths, while others add maps, heroes, upgrades, and elaborate progression systems.