Come on. Facebook and twitter APIs are so restricted you can't even build a usable alternative client (look at all twitter clients that we had a few years ago, they are all gone now).
Facebook won't even let you read public events through their API anymore, public events created by businesses that want the public to attend, that are visible to anyone even if they're not logged in, that are easily searchable through Google.
But that's probably because the same day they removed that events API, they launched the Facebook Local app that shows all the events around you. Can't have anyone competing with your app.
Facebook and Twitter have public APIs.