I don't like tower defense games ... but Ant Buster is awesome!

Check it out, maybe try to make an offline port.
http://armorgames.com/play/522/antbuster

It's about:
The starts off and continues decently where ants come out of their nest and try to make their way to your pie. There are many types of up/down-gradable "Ant Killers" and placing specific types in specific places can give you huge advantages like killing them efficiently or making the ants walk an unnecessary long distance. On the way to the pie, they either die or they sustain damage. If they get to the pie, they completely heal and try to walk back to the nest. You can highlight the ant (only one) for your towers to take aim and destroy if it falls in its range. If they succeed, they win that pie, if the ant dies the pie returns to the platter and there are several peices. After a while you notice the game is very difficult and that you have to familarize yourself with all the weapons, tactics and start a fresh new game without making mistakes and spending your money wisely and as soon as possible.