Almost every operating system (OS) has its own package manager to install a new software in a manageable way. Let's say you want to use git on a Ubuntu 14.04 Linux OS to download your source code repository from GitHub; you will issue the following command:
apt-get install git
The apt-get command will search for the git package in its package repository server and download the dependency graph, and packages on top of git will be built. It will issue install commands for each package in the graph using the dpkg utility, run the following command:
$ apt-cache rdepends git
Running the preceding command lists out all dependencies of git, which is over 100 packages! Clearly, it's humanly impossible to install these dependencies in the correct order by hand without losing sanity.
For almost all platforms, whether a programming language...