Apple IIGS Toolbox Reference, Volume 1
Apple IIGS Toolbox Reference, Volume 2
Apple IIGS Programmer's Workshop Reference
Apple IIGS Programmer's Workshop Assembler Reference
Apple IIGS Programmer's Workshop C Reference
ProDOS 8 Reference
Apple IIGS ProDOS 16 Reference

Apple Human Interface Guidelines
Applesoft BASIC Programmer's Reference
Applesoft BASIC Programming with ProDOS
Programming the 65816 by David Eyes and Ron Lichty. New York: Brady Communications (a division of Simon & Schuster), 1986.
The C Programming Language by Brian W. Kernigham and Dennis M. Richie. Englewood Cliffs, N.J.: Prentice Hall, 1978.
Apple IIe Technical Reference

Reference manuals

165