People tweeting stuff. We allow tweets from anyone.
RULES:
Insecure people would download this app, and prematurely 'cancel' all their plans so that they get notifications the moment anyone uses it. This app idea only works with the pretense of privacy until both parties agree, but it is open to manipulation. And once you know that manipulative people are misusing the app, you will police your usage of it, and then we're back to square one, where people are unwilling to communicate.
In all honesty, I would probably be one of those people because I hate the idea of someone hanging out with me just because they are obligated to.
I prefer the backup plan. I schedule secondary commitments a few hours after the first one, so I have a reason to bail if it's not going well. If it's going great, I cancel the (less important) backup.
That sounds like you have friends that you cancel a lot on. Most people I know just stop inviting them to do things when they usually refuse. Because that's usually a sign.
There is no such thing as an introvert. Only people that don't know they are cool yet.