They are tools for managing multiple installed versions of a programming language. When developing software, we often specify dependencies using version numbers, which indicate the version of the language or library that should be used when running the software. Running the software with the specified language runtime or library version ensures that the expected features of that library or language runtime are available and also helps avoid unexpected issues related to differences in the environments, including different developer&#x27;s local systems as well as remote server environments.<p>In the case of a programming language runtime, if you have one project that&#x27;s configured to use version 2.2.4 of a language and another that&#x27;s configured to use version 2.1.0, these tools provide an easy way to install and switch between the two versions.<p>This is not unique to Ruby, and similar projects exist for other languages. For example, nvm (<a href="https:&#x2F;&#x2F;github.com&#x2F;creationix&#x2F;nvm" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;creationix&#x2F;nvm</a>) and n (<a href="https:&#x2F;&#x2F;github.com&#x2F;tj&#x2F;n" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;tj&#x2F;n</a>) provide something similar for Node (JavaScript), gvm (<a href="https:&#x2F;&#x2F;github.com&#x2F;moovweb&#x2F;gvm" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;moovweb&#x2F;gvm</a>) for Go, and multirust (<a href="https:&#x2F;&#x2F;github.com&#x2F;brson&#x2F;multirust" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;brson&#x2F;multirust</a>) for Rust.