VScript, introduced in Left 4 Dead 2, is a virtual machine for scripting that acts as an abstract binding layer between the Source engine and external scripts. According to the Alien Swarm SDK, the following scripting languages are, or could be supported in the near future:
Script files are placed and executed in
scripts/vscripts/ inside the game folder.
- Alien Swarm: Reactive Drop
- List of Script Functions
- Portal 2 (Client/UI only)
Main article Vscript Fundamentals