This TD idea was submitted by tman. You can familiarize yourself with flash tower defenses here.

tman’s Idea:
I have two thoughts, a World War II simulation. You could build machine gun turrets, gernades, flame throwers, nuclear bomb etc.

Instead of taking lives from the last point either you gain or lose ground (kind of like tug of war) if you gain all the territory you win, lose it and you lose.

Another idea is to reverse the roles, have a preset path with towers defending it, only the player chooses the number and creatures to send in and attack the exsisting towers. Player would receive money based on the amount of damage they incurred on the towers and getting through the maze. At the end of each round the tower could automatically upgrade, and the player could choose upgrades, number of attackers, attacker strength, weapons etc.