I'm confused.... where is it? Comparing portfolios

There is an online tool where you can enter up to 3 lists of stocks and it will show you the difference in performance of each. It give the historical performance based on how far back in time you tell it to look. you can put in how much investment you had made and. It is a FREE tool and does not require premium access to the website.  I think there is a name for the tool but I can't remember what it is and I have tried for hours to find it and I can't and would appreciate someone telling me all about it