Alarameth TD runs on the Unity game engine (by Unity Technologies). Unity is one of the most powerful and most versatile game engines in the industry today, used in other popular games such as Deus Ex: The Fall (Eidos) and Hearthstone: Heroes of Warcraft (Blizzard Entertainment).
Unity's focus on cross-platform support, strong development tools, and use of cutting-edge technologies made it a clear choice for the development of Alarameth TD.
The Unity3D website can be found here.
Many assets were sourced for various aspects of the game. Unfortunately, going into detail about each would fill a novel so they're simply listed below.
Whether it was a creature, a building, a special effect, an editor tool, or even something as simple as a tree or rock, these fantastic assets helped to bring the game experience to a whole new level.
The vast majority of the assets created by the above individuals/companies can be found on the Unity Asset Store. The remainder have sites which can be found with a little searching.