Desktop Tower Defense

http://www.handdrawngames.com/DesktopTD/game.asp

Tower Defense or short TD is a subgenre of strategy games and its gameplay mechanism was based on a series of maps for StarCraft called the Turret Defense.

In this flash adaption, Desktop TD, the player has to stop invaders from crossing through the player's fortress. The player can buy turrets that kill the invaders and set them up in a maze to optimize his defense tactics.

The game seems to be updated frequently, so be sure to check back once in a while!