A program that automatically explores the World-Wide Web by retrieving a document and recursively retrieving some or all the documents that are referenced in it. This is in contrast with a normal web browser operated by a human that doesn't automatically follow links other than inline images and URL redirection. The algorithm used to pick which references to follow strongly depends on the program's purpose. Index-building spiders usually retrieve a significant proportion of the references. The other extreme is spiders that try to validate the references in a set of documents.
Crawlers are usually very expensive for personal use but are VERY powerful tools for marketing.
FalconsEyes is the perfect tool for fast crawling into a list of defined websites, sorting all email addresses found in those web sites and collecting them in a local text file. Today there are millions of e-mail addresses now available on the World Wide Web. Install FalconsEyes and use it as long as necessary for you to see how valuable it can be to you. The demo version of FalconsEyes is almost fully functional. The restrictions of the demo version are that it's impossibile to save collected info .