These are excellent if your wanting to generate a certain tone and keep it going if desired.......http://www.wavtones.com/functiongenerator.php
Just enter the tone you want and how long you want it AND A FILE IS DOWNLOADED TO YOU!!!!!!
I entered 528 for 100 seconds (SINE) (8.41M (I dunno if there is a limit or not on the duration))
This is a DOS application that lets you generate from 1-22050Hz and is quite small!http://advsys.net/ken/util/heartest.exe
To use it: OPEN A COMMAND PROMPT AND GOTO THE DIRECTORY YOU PUT IT IN AND TYPE "heartest" and it pops up on your screen!