Garry's Mod 13 review

Sandbox games were 2012’s big thing, with indie world builder Minecraft achieving a level of support that bordered on the fanatical. It encouraged copycats from bedroom developers and big names alike, but one major update to an old school sandbox went unnoticed. We’d like to change that.
Garry’s Mod - the sandbox built on Half Life 2’s game engine - has been rebuilt from scratch. First launched in 2006 the game turns Half Life 2 and Team Fortress 2, into a virtual construction kit. Originally based on the Valve’s Source engine, Garry’s Mod 13 has it’s own compatible rendering engine - ridding the module of many bugs and enabling it to be used without Half Life 2.
Sandbox games give users control over virtual worlds. In Minecraft’s case, builders have blocks composed of different elements that enable them to craft landscapes and create buildings. In Garry’s Mod, the elements are determined by the entities and maps extracted from HL2 and TF2. 
Play begins, in single player mode, with the selection of a map from either of those games. Hints are enabled automatically and a bubble will pop up urging you to press and hold “Q” on your keyboard. This opens a dialogue full of game elements, from none-player characters (NPCs) to weapons and furniture.
The main attraction of Garry’s Mod is the realistic - or unrealistic - simulation of physics in a virtual world
When you place items in the maps, you have two special “weapons” to manipulate the world. The “Physics Gun” enables you to pick up and move items. It’s a multipurpose tool that, when used with NPCs, allows you to position their limbs and bodies and then freeze them into place.
The second special weapon is the “Tool Gun”, which is actually a number of different weapons all rolled into one. You can select what the Tool Gun does by selecting “Q” and choosing a function. This turns Garry’s Mod from a doll’s playhouse into a full construction set, with settings that enable you to create motors, winches, elastic ropes and more. The Tool Gun can also be used to finely tune the positioning of NPCs, with face, eye and finger posers.
How you actually use Garry’s Mod is up to you. Some build impossible structures, others create new games from the building blocks provided. A key, emerging use is virtual photography - screenshots capturing action that would be impossible to snap during the cut and thrust of a normal game.
Like the Valve games that Garry’s Mod was built on, it can be expanded. The Steam Workshop features additional tools and game modes, models and maps that you can download and use with Garry’s Mod.
There’s a multiplayer mode too - just like Half Life 2. The number of different game types in this mode is a testament to the inventiveness of the community. There are role-playing servers, zombie survival games, capture the flag, collaborative building servers, racing games... The list goes on and on.