GNS3 is used by hundreds of thousands of network engineers worldwide to emulate, configure, test and troubleshoot virtual and real networks. GNS3 allows you to run a small topology consisting of only a few devices on your laptop, to those that have many devices hosted on multiple servers or even hosted in the cloud.
GNS3 is open source, free software available on http://www.gns3.com. The first was released in 2008.
For a long time most of the documentation was not something made by us. A lot of ressources is available online (youtube, paid courses, books) made by community members. But this year we decided to put a big effort and getting something good.
You could found the documentation here: http://docs.gns3.com/. We are very happy with Docsearch because it was so simple to integrate and the fact that the search support anchor location is just awesome.