Lua

Lua is a lightweight high-level programming language designed primarily for embedded use in applications. It is used in the Scribunto extension, which allows the creation of modules in MediaWiki. A tutorial to create a Lua module can be found here.

Yesno
Yesno originates from the English Wikipedia and allows for consistent treatment of boolean-like input. For example, an input of y, yes, 1, or true would be classified as true, but n, no, 0, or false would be classified as false. It is not designed to be invoked directly, but is designed to be "required" in another Lua module that is designed to be invoked directly.

No globals
No globals causes a Lua error if any nil global is read or if any global is written to, with the exception of "arg". The "arg" variable is excluded because it is necessary for Scribunto's "require" function to work properly. It is very useful in some cases, as seen from the fact that the module is used on roughly 33% of all pages on Wikipedia. It is commonly noticed that if a page on the English Wikipedia has at least one template, there is a very high chance that template uses No globals.