Doomsday Engine

Remote repositories. Similar to apt repositories, web servers can set up a specific directory structure that Doomsday can then access to read a compilation of the available package metadata and download individual packages. Interestingly, thanks to (upcoming) FS2 remote folders, clients can access the server's local package cache as if it was a remote repository where packages can be automatically downloaded if necessary.

Virtual repositories. A remote repository that looks like a regular remote repository to Doomsday, but in fact is something different like the idgames archive, where all the WADs are made available as if they were Doomsday packages so that they are accessible via the same mechanism as any other package.