Guest's Login app is a great way to replace your default landing page with activity feed. App creates a page that looks the same as home page for your existing users and shows it for guests (of course with posting limitation). In this way guests will be able to preview latest activity of your network.
The app works best for networks that are not friends-only community (in case if friends-only community setting is turned on, guest's feed will be empty, as all feeds in the network are private).
Feedback from one of current app users:
The guest feed is our 1# traffic generator, it's pushed our alexa rank to under 50k in the us.