Wikipedia
Libraries.io is an open source web service that lists software development project dependencies and alerts developers to new versions of the software libraries they are using.
Libraries.io is written by Andrew Nesbitt, who has also used the code as the basis for DependencyCI, a service that tests project dependencies. A key feature is that the service checks for software license compliance.
As of 25 July 2016, the web service monitors 1,584,130 open source libraries and supports 33 different package managers. To gather the information on libraries, it uses the dominant package manager for each programming language that is supported. The website organizes them by programming language, package manager, license (such as GPL or MIT), and by keyword.
The code that runs the web service is available on Github and under the GNU Affero General Public License.