link http://www.ninjatown.com/ here

It's basically a tower defense game, but it's not so straightforward and simple. Well, it IS simple AND straightforward, but it's not boring. You build buildings that Ninja's come out of and they fight lil demon things or something. There's like, a forest Ninja and a Business Ninja (game says they have years of caffeine addiction, so they are fast), and it's rad. The plot is that this evil guy is trying to steal the Ninja's secret Ninja Cookie recipe. awesome. It's actually really funny and clever, as if they actually spent time writing the dialog (!).
Fun game. I recommend it.
