Parse	Let's you control what the user typed in at the command line.
Form	Get access to the all answers right before they're displayed.
Exec	Mess with the two variables being calculated.
Expr	Gives you control over the equation numbers right before they're printed on the graph screen when graphing.
Home	Run your own routine right before the calculator returns to the homescreen.
CmdTok	Executed right before any TI-BASIC functions (DelVar, Asm, Bin, etc.) are run.
Key	Probably the most popular, have the calculator run your program every time _Getkey is called.
Grf	Implement your own routine right before graphing functions.