Main predicates:

Control predicates
Strawberry functions
Loops predicates
Execution control
Input and Output predicates
Dialogs
Knowledge base manipulation
Direct Database Manipulation
File Manipulation:
Time
Special effects
OLE and ActiveX
E-mail control
Prolog CGI Scripts
Sockets support
SQL support

Arithmetic and special types:

Type checking and conversion predicates
Comparison
Evaluation
Standard arithmetic
Strings
Char Sets
Bitwise functions
Floating point functions

Windows and Drawing:

Windows and Controls creation
Windows and Controls use
Menu
Checkbox
Edit methods
Drawing
Fonts, colors, pens and backgrounds
Timer
Clipboard