Some browsers (including Thunderbird and Internet Explorer) have the ability to file URLs by categories.
Some also have the ability to attach many keywords to each URL they save, and therefore file some of the URLs in multiple categories.
Assigning URLs to categories this way is manual. Are you asking for it to be automatic instead?
I've found Google searches adequate for finding URLs, if I can think of suitable keywords to specify what type of URLs I want to find.
Boundation?