The scripting engine provides a set of 'System Functions', usually preceded by sys. Below is the complete list of system functions currently available.

(Note also the list of special system control functions which includes special cases like the 'Sleep' function etc)

Text Functions
Player Information
Inventory and Wealth manipulation
Building Information
World map functions
ConstructionFunctions
Scripted Subgames
Building Ownership
Town information and control
Maths Functions
Misc. other functions

For a full(ish) alphabetical list of script functions : Alphabetical Function List