Hi @nicolechan – sorry for not getting back to you earlier.  I think the app you are thinking of Booshaka in your #2 question.  I’m not sure where you want to add the invite friends button – on the top of an App?  I don’t know of one offhand – I have found a tutorial on how to invite your friends via a coded app you can put on a website:   http://www.9lessons.info/2012/07/facebook-invite-friends-api.html   And you can probably add that to a custom tab on your page too.  

Then I wrote a post about some free Facebook apps here: http://www.socialmediaexaminer.com/top-10-facebook-apps-for-fan-engagement-and-building-community/  

Hope that helps!  Anyone else have any good Facebook Apps that you like?

Hi Nicole Chan,

i think this two links should be useful for you,
For Login with facebook using php sdk, http://www.idiotminds.com/login-with-facebook-using-php-sdk/

For Invite Friends with Facebook app,http://www.idiotminds.com/invite-friends-with-facebook-using-php-sdk-and-javascript-sdk/