Garry's Mod

Garry's Mod is a ten dollar sandbox program running on Valve's Source engine. Being a sandbox, it has great potential for making art like what i have shown in a previous post, as well as movies, and also functions as a game through the massive amount of user-generated content, game modes, props, and maps, in addition to free online multiplayer via Steam. It started from humble beginnings, as a free sandbox mod for Half-Life 2. As Valve expanded their Source engine and it's repertoire of games, the mod expanded with it, eventually being officially licenced and supported by Valve, leading to it being sold on Steam for $9.99 USD (it goes on sale a lot too). All that's required is an installed source game (Team Fortress 2 is available for free) and the mod itself. the mod also includes most of the content from Half-Life 2, without requiring it to be installed, however for content from Left 4 Dead, Half-Life Source, Counter Strike Source, and some other games, a purchase of those games is required. All in all, a great value for ten bucks.