The Source engine is a 3D game engine developed by Valve Corporation. Its unique features include a large degree of modularity and flexibility, an artist-driven, shader-based renderer, accurate lip sync and facial expression technology, and a powerful, efficient and completely network-enabled physics system.
Amazing! I have made so many maps using this! 10/10! So Easy to use too! It can be used to make so many different types of maps! I would definitely recommend it to other people who are looking for a easy way to make maps!