GitHub

GitHub is a web-based version-control and collaboration platform for software developers. Microsoft, the biggest single contributor to GitHub, initiated an acquisition of GitHub for $7.5 billion in June, 2018. GitHub, which is delivered through a software-as-a-service (SaaS) business model, was started in 2008 and was founded on Git, an open source code management system created by Linus Torvalds to make software builds faster.

Git is used to store the source code for a project and track the complete history of all changes to that code. It allows developers to collaborate on a project more effectively by providing tools for managing possibly conflicting changes from multiple developers. GitHub allows developers to change, adapt and improve software from its public repositories for free, but it charges for private repositories, offering various paid plans. Each public or private repository contains all of a project's files, as well as each file's revision history. Repositories can have multiple collaborators and can be either public or private. 

GitHub facilitates social coding by providing a web interface to the Git code repository and management tools for collaboration. GitHub can be thought of as a serious social networking site for software developers. Members can follow each other, rate each other's work, receive updates for specific projects and communicate publicly or privately. 

Three important terms used by developers in GitHub are fork, pull request and merge. A fork, also known as a branch, is simply a repository that has been copied from one member's account to another member's account. Forks and branches allow a developer to make modifications without affecting the original code. If the developer would like to share the modifications, she can send a pull request to the owner of the original repository. If, after reviewing the modifications, the original owner would like to pull the modifications into the repository, she can accept the modifications and merge them with the original repository. Commits are, by default, all retained and interleaved onto the master project, or can be combined into a simpler merge via commit squashing.   

Because GitHub is so intuitive to use and its version-control tools are so useful for collaboration, nonprogrammers have also begun to use GitHub to work on document-based and multimedia projects. GitLab is an open source alternative to GitHub.