Search the Invisible Web: 20 Free Resources

The Wayback Machine is a deep web tool that holds a vast number of web pages, over 300 billion, in fact. As part of the nonprofit Internet Archive, the Wayback Machine has decades of web pages archived and accessible to anyone.

Not only are websites stored there but also books, audio recordings, concerts, videos, television news programs, images, and thousands of software programs.

Another invisible web searcher is available at USA.gov, a mammoth search engine and portal that gives you direct access to a wide variety of information and databases from the U.S. government, state governments, and local governments.

USA.gov includes access to the Library of Congress, an A-Z government agency index, the Smithsonian, and much more.

The WWW Virtual Library includes hundreds of different categories and databases on a wide variety of subjects, ranging from agriculture to international affairs.

The site claims that the WWW Virtual Library is the oldest catalog of the web, started by Tim Berners-Lee, the creator of HTML and of the World Wide Web itself, in 1991 at CERN in Geneva.

The website is run by volunteers who compile pages of links for particular areas in which they have expertise. The Virtual Library's deep web pages are among the highest-quality guides to specific sections of the web.

Science.gov searches over 60 databases and more than 2,200 selected websites from 15 federal agencies, offering 200 million pages of authoritative U.S. government science information, including research and development results. 

The Science.gov website is an interagency initiative of several U.S. government science organizations. These agencies form the voluntary Science.gov alliance, which governs the site.

Wolfram Alpha is a computational deep web search engine, which means it stores a vast amount of pure data available to you by search and by a question-and-answer format.

The website aims to collect and curate all objective data; implement every known model, method, and algorithm; and make it possible to compute whatever can be computed about anything.

The National Security Archive at George Washington University is another free invisible web search tool that's home to a treasure trove of declassified documents, papers, and other primary-source materials on subjects related to U.S. national security, foreign policy, intelligence policy, and diplomatic and military history.

The site was founded in 1985 and is home to decades worth of documents released under the Freedom of Information Act. 

Alexa provides analytical information about web properties that's so specific that no regular search engine can compile it. The service gathers much of its traffic data from direct sources in the form of sites that chose to install the Alexa script to certify their metrics.

The traffic estimates on Alexa are based on data from a global traffic panel, which is a sample of millions of internet users using one of thousands of different browser extensions.

Website owners especially can benefit from the data that Alexa offers; for example, here's a list of the top 500 sites on the web. 

The Directory of Open Access Journals (DOAJ) is an invisible web resource that indexes and provides access to quality open access, peer-reviewed journals. Thousands of journals and millions of articles are searchable using the DOAJ. 

The Directory of Open Access Journals indexes research journals, periodicals, and their articles' metadata. The DOAJ aims to be comprehensive and cover all open-access scientific and scholarly journals that use an appropriate quality control system. The directory's goal is to increase the visibility and ease of use of open-access scientific and scholarly journals—regardless of size and country of origin.

The Online Books Page, a deep web service offered by the University of Pennsylvania, gives readers access to more than two million books freely accessible (and readable) on the internet. Visitors also gain access to significant directories and archives of online texts, as well as special exhibits of particularly interesting classes of online books.

One of the most vivid and interactive sites on this list of invisible web resources, the Library of Congress offers an incredibly rich and varied array of content. Collection highlights include congressional records, digital preservation resources, the Veterans History Project, and the World Digital Library.

According to the site:

The Library of Congress is the nation's oldest federal cultural institution and serves as the research arm of Congress. It is also the largest library in the world, with millions of books, recordings, photographs, maps and manuscripts in its collections.

If you're looking for data not found in your typical search engine, Census.gov is one of the first places you'll want to visit. From geography to population statistics, you'll be able to find them on this website.

The U.S. Census Bureau conducts demographic, economic, and geographic studies and strengthens statistical development around the world through technical assistance, training, and software products.

For decades, the Census Bureau has performed international analytical work and assisted in the collection, processing, analysis, dissemination, and use of statistics with counterpart governments in over 100 countries.

Copyright.gov is another U.S. government resource you can put in your invisible web search toolbox. Here, you can view works registered and documents recorded by the U.S. Copyright Office since January 1, 1978, as well as search records of registered books, music, art, periodicals, and other works, including copyright ownership documents.

The Catalog of U.S. Government Publications gives deep web surfers instant access to electronic and print publications from the legislative, executive, and judicial branches of the U.S. government, with more than 500,000 records generated since July 1976. 

PubMed, part of the National Center for Biotechnology Information, U.S. National Library of Medicine, is the perfect invisible web resource for anyone who's looking up medical or medical-related information. It offers more than 29 million citations for biomedical literature from MEDLINE, life science journals, and online books. 

The FAA Data and Research pages offer information on how FAA research is done, the resulting data and statistics, and information on funding and grant data. Anything from aviation safety to unruly passengers (seriously) can be found here. 

DuckDuckGo searches both the regular web and the deep web without saving any of your personal information or your search results. DuckDuckGo blocks advertising trackers to keep your search history private.

Although DuckDuckGo resembles other search engines—and a simple one at that—it's fully capable of performing advanced searches on the deep web. 

FindLaw is a gigantic repository of free legal information on the internet, and it offers one of the largest online lawyer directories available. You can use FindLaw to locate an attorney, learn more about U.S. law and legal topics, and participate in the active FindLaw community forums. 

The online Louvre museum begs to be discovered and cherished by art lovers all over the world. View thematic collections of art, get more information about the background of selected works, and view art aligned with historical events.

Economic Indicators on Economy.com gives users quick access to free economic, demographic, and financial data. It provides comprehensive and extensive historical and forecast data at the national and subnational-regional levels representing over 93 percent of global GDP.

Economy.com's Indicators covers more than 180 countries, over 150 global metro areas, and all U.S. states, metro areas, and counties. The databases contain economic, financial, demographic, and consumer credit time series.