The Hλlf Life² mod is an amazing sandbox for $9.99 on steam. Garrysmod 10 (by Garry Newman) inspired many Half life 2 comics like Concerned, which takes place before 
and during Gordon Freemans arrival in the actual game. It allows to use a variety of tools to create almost anything, and features a download site where users can download custom content, like props, tools or weapons to enhance the possibilities of things to do. Th
e main things done on Gmod is posing character ragdolls, creating contraptions, making scenes and just messing around. At the end, you can take snapshots using another the picture 
tool
and during Gordon Freemans arrival in the actual game. It allows to use a variety of tools to create almost anything, and features a download site where users can download custom content, like props, tools or weapons to enhance the possibilities of things to do. Th
e main things done on Gmod is posing character ragdolls, creating contraptions, making scenes and just messing around. At the end, you can take snapshots using another the picture 
tool