With the free demo of Build&Defend, you can play up to the first boss of the Survival mode.
With the full version of Build&Defend, you get access to the entire game, and you get your own dog! Also, you get access to several mini games (Epidemic, dungeon, etc.), unique items, unique weapons, towers and new monsters. You can also change (and draw) the skin of your player.
In addition, with the full version of Build&Defend, you can also play with up to 4 of your friends on the same computer (every player with its own joystick), and with up to 12 people on internet.
After you purchased the game, you will receive a game key on your Paypal e-mail address. You can use this key to activate your account, or you can send the key to one of your friend as a gift :).