There's also http://socialwifi.com, not sure if they provide an option to spam the user's timeline or not.
Source: I used to be involved with a WiFi company that offered Facebook "login".
Edit: clarified my involvement
Unless you're Facebook, I guess: https://www.facebook.com/business/facebook-wifi
>After checking in, people will be asked if they also want to like your Page so you can continue to connect with them on Facebook.
Of course, if using Facebook WiFi, you do check-in to the location which triggers a host of other "features" within your Facebook account and experience. Similar to if you check-in to a location with the standard Facebook App.
I can see the argument that it's an extension of that experience, while providing WiFi service in exchange for it.
This is a service provided by Facebook: https://www.facebook.com/business/facebook-wifi