The TI-88 calculator contains a large number of functions accessible through the OP key. The manual lists them all, but there appears to be a slight discrepancy between the manual and the OP codes on the prototype that's in my possession. Here's a list of all TI-88 OP codes that work on the prototype:

OP 00		List OP code definitions
OP 01		Set calculator to default operating modes
OP 02		Display calculator settings
OP 03		Recall last error message
OP 04		YES/NO/UNK/ENT/CONT cue instruction for programs
OP 05		YES/NO cue instruction for programs
OP 06		ENT/CONT cue instruction for programs
OP 07		CONT cue instruction for programs
OP 08		List ALPH key second functions
OP 09		Recall alpha display register
OP 10		Right circular shift of alpha register
OP 11		Left circular shift of alpha register
OP 12		Show all 13 digits
OP 13		Round display register
OP 14		Unformatted display mode of 16 BCD digits
OP 15		Cancel unformatted mode
OP 16		Hexadecimal mode
OP 17		Decimal mode
OP 18		Display system flag definitions
OP 19		Display flags that are set
OP 20		Save user flags into an internal hierarchy register
OP 21		Exchange saved and current user flags
OP 22		Set pause timing to default
OP 23		Set pause timing
OP 24		Turn on implied multiplication mode
OP 25		Cancel implied multiplicatio mode
OP 26		Absolute value function
OP 27		Signum function
OP 28		Convert D.MMSS to decimal degrees
OP 29		Convert decimal degrees to D.MMSS
OP 30		Display current angle mode
OP 31		Convert degrees to radians
OP 32		Convert radians to degrees
OP 33		Convert radians to grads
OP 34		Convert grads to radians
OP 35		Convert grads to degrees
OP 36		Convert degrees to grads
OP 37		Clear statistical registers
OP 38		Compute Y-intercept and slope
OP 39		Compute correlation coefficient
OP 40		Compute Y estimate
OP 41		Compute X estimate
OP 42		Compute statistical means
OP 43		Display number of data entries
OP 44		Compute standard deviation (N)
OP 45		Compute standard deviation (N-1)
OP 46		Set program counter to display value
OP 47		Copy program instruction code to display
OP 48		Copy display to program instruction
OP 49		Set default partitioning
OP 50		Set partitioning
OP 51		Soft partitioning
OP 52		Hard partitioning
OP 53		List program labels
OP 54		Calculator system test 1
OP 55		Calculator system test 2
OP 56		Read tape file into main memory
OP 57		Write main memory contents to tape
OP 58		Read tape file into program memory
OP 59		Write program memory contents to tape
OP 60		Read tape file into data memory
OP 61		Write data memory contents to tape
OP 62		Read numbered module file from tape
OP 63		Write numbered module file to tape
OP 64		Convert decimal to hexadecimal
OP 65		Convert hexadecimal to decimal
OP 66		Test module number
OP 67		Test module status
OP 68		Number the module in the primary port
OP 69		Erase the module in the primary port
OP 70		Read module program into program memory
OP 71		Write program memory contents to module
OP 72		Protect module
OP 73		Copy module
OP 74		24-hour mode
OP 75		12-hour mode
OP 76		Add time values in HH.MMSS form
OP 77		Subtract time values in HH.MMSS form
OP 78		Set alarm time
OP 79		Turn alarm on
OP 80		Turn alarm off
OP 81		Sound a tone
OP 82		Turn on tone on error
OP 83		Turn off tone on error
OP 84		Turn on tone on cue prompt
OP 85		Turn off tone on cue prompt
OP 86		Output data*
OP 87		Input data

*The manual lists OP 86 as an instruction that turns on keyboard tones. However, on the actual prototype this instruction is omitted, and the remaining two OP codes are shifted down by one.