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
Entity Functions
Misc. other functions

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

Text Functions
For providing names of items, players, skills etc; converting names to IDs and vice versa
Player Information
Get information about the player ; what skills, inventory, health they have etc
Inventory and Wealth manipulation
Add items and wealth to the player
Building Information: Provides information about a building and its contents (and functions to change the building UI)
World map functions: Get map coordinates for items in the world, convert map to world coordinates and vice versa
ConstructionFunctions
For construction of buildings and other permanent or transient items on the world
Scripted Subgames
System for creating and controlling subgames which groups of players can participate in
Building Ownership
Querying and controlling the ownership status of buildings
Town information and control
Info about towns and functions to modify the status of town buildings
Maths Functions
Maths functions such as rand, sin, cos etc
Entity Functions
System for creating 'entities' in the world - these are models/objects that you can control from script, including the ability to set off standard behaviours such as 'attack the player' Misc. other functions
General other uncategorised bits