Just wanted to know if there is an online tool that shows a website most popular pages from highest to least.
I don't know of any tool that does this, and if someone claimed to, I'd be highly skeptical. Compete/Quantcast/Hitwise can't even get it right for an entire domain, let alone a page.
That said, SEMRush may be able to help you identify which specific pages rank highly for certain high traffic keywords, which would approximate what you want.
If you mean for another website that is not yours, then no, there is no way to get this information. This information is only available if you have tracking software on a website's web pages or access to the site's access logs.
There is no way of reliably analysing the traffic being driven to pages of another website unless you have access to their analytics software.
There are tools that attempt to estimate the traffic statistics of other pages with data gathered through toolbars, browsers, search engines, etc that they have control over. Chances are this information won't be very reliable unless you have en extremely large user base to sample your data from - and even then it's still not everyone.