[juliangoldsmith]

All of the code for the UI, server-side game logic, and client-side game logic in Quake 3 was run in the VM. It allowed code to be stored with game data, and client-side mods to be safely downloaded directly from the game server.

The link in the sibling post has most everything you'd ever want to know about it.

[hinkley]

It might be worth mentioning that there’s a long tradition of this pattern in game design. In quite a few cases, much of the game logic is separated from the graphics engine, in a simpler language with an interpreter.

In the case of world of Warcraft, the Lua interpreter allowed for a rich ecosystem of UI (and light behavioral) addons. In some cases very popular addons features were added into the core UI in later updates.

I find that arrangement pretty compelling. In the few cases where I’ve worked on or with a team with addon support I bring this up: use the community sourced features as a popular vote for what to incorporate (just be sure to reward the author somehow).