Dependency Supervisor.
This is basically (in its current scope) a wrapper around Elixir's (>= 1.6) DynamicSupervisor. However, making DepSup as a seperate library helps in situations where you need to "break" out of the dependency graph.
For example, when wrapping ejabberd within an Elixir project and extends it through "Modules", it's tricky to have runtime dependencies (i.e. other processes that the module code depends on) because ejabberd will start first before the Elixir wrapper application, so putting extra processes in the application's root supervisor is not enough, you have to wait for them to be started - again, because ejabberd modules will be started before the wrapper application. By extracting this DepSup concept to a separate library we can arrange it to make sure it starts up before ejabberd, which provides many support for managing any runtime dependencies that later applications (or "modules") might require.