A significant amount of what the federal government "does" isn't technically done by the federal government. Instead, it's done by private companies working under contract. Thousands of contractors provide goods and services to the federal government, and it's the job of the Federal Acquisition Service to keep track of them all. That agency maintains an online database of all current federal contractors.
Finding the List of Contractors
The Federal Acquisition Service is a unit of the U.S. General Services Agency. The master list of federal contractors is available on the GSA's online "eLibrary," which can be accessed by following the link in the "References" section.
Clicking a company's name in the list of contractors takes you to a page with details about the company and the contract. This includes the company's address, telephone number and website; the e-mail address of a designated contact person for the company; the phone number and e-mail address of a federal official designated as the company's liaison with the government; the contract number; a general description of the category the contract falls under; and the date on which the contract ends.
Laws passed by Congress give certain businesses preference over others when it comes to awarding certain contracts. For example, small businesses, companies owned by military veterans or women and companies based in disadvantaged areas may get extra consideration during bidding. Each contractor's page specifies whether the company fits into any categories that might qualify for preferences.