Onslaught2 is a tower defense game in which you try to defend your base from being overrun by aliens. After you select the mode you wish to play on, (easy, medium or hard), choose one of the 12 maps and start spending your cash to buy and strategically place your towers. There are four towers to select from, each having an array of upgrades which expand the towers' capabilities. You can pause the game at any point to make your purchases and upgrades.
On the downside, alien numbers, strength and speed increase fast and you have only 10 lives before game over.