ASDF-System-Connections provides auto-loading of systems that only make sense when several other systems are loaded. If I'm lucky, an example will make this clear! CL-Containers and CL-Variates are separate systems and can therefore be loaded independently. If both of them are loaded, however, then it makes sense to also load code that uses CL-Variates to sample random elements from containers. Rather than requiring you to remember to load that extra system (and to load it only after both Cl-Containers and CL-Variates are loaded), ASDF-System-Connections lets you set things up so that loading happens automatically.
Here is a simple example from metabang-bind's system definition:
(asdf:defsystem-connection bind-and-metatilities :requires (metabang-bind metatilities-base) :perform (load-op :after (op c) (use-package (find-package :metabang-bind) (find-package :metatilities))))
The requires clause specifies the other systems that must be loaded before this connection will be activated. The rest of the system definition is regular ASDF. ASDF-System-connections will be loaded as soon as the systems they require are all loaded and they will only be loaded once. Before loading a system that uses a system connection, you should load ASDF-System- Connections in the usual manner:
(asdf:oos 'asdf:load-op 'asdf-system-connections)
the current ASDF-System-Connections repository is on github and you can clone it using:
git clone git://github.com/gwkkwg/asdf-System-Connections
Its CLiki home is right where you'd expect.