Defenders of Ardania is a tower defense game from Paradox entertainment. You have to balance building towers to defend yourself with the need to make troops to take out the enemy. All of these actions require either mana or gold, both of which slowly regenerate automatically. The area between you and your enemy is a grid that allows for multiple paths for units to move towards their targets. Towers can be built on any tile with a tower drawn onto it and a tower already built nearby.
Units will take the shortest path possible to their destination but you can block them with towers. There are three factions to choose from and 8 towers and units for each faction. Obviously some towers are better at killing a specific unit than others so you have to react to what your opponent is producing. If you have a specific strategy in mind, you can put some of your gold into research which can decrease the price of towers or units.
There are PC, PSN, and XBLA versions of the game planned with a price range of around 10 to 20 dollars still being worked out. PSN and XBLA versions are planned but not confirmed because they still have to work out the details with Sony and Microsoft. An iPad version is being worked on, but it will only have single player while the other versions have multiplayer with up to 4 people. Look for this game to release in June on iPad and PC, with a XBLA and PSN release later down the road.