A set of tools from Google for applying performance best practices to web pages.
A tool written by Yahoo! that analyzes web pages and suggests ways to improve their performance
"Imho pagespeed is better than yslow"
from question "Tool for measuring html5 performance(YSlow or PageSpeed)"
"In my testing so far google s pagespeed addon is far and above much better than yslow"
from question "Fast Loading web pages"
"I use firefox with firebug and yslow and think it s more reliable than pagespeed"
from question "Facebook is not compressing Java Script files used in Like and Comment Plugin"