I'll start...
https://speakerdeck.com/chadokruse/10speak-pitch-deck-the-mobile-calendar-public-domain
Idea: The mobile calendar isn't about what's on your calendar, it's about what's NOT on your calendar.
Reason for not continuing: I woke up one day and realized the app I was creating wasn't really making the world a better place. I'm now working on something I'm truly passionate about (fixing philanthropy). Also, ran out of money before validating the right go-to-market strategy.
Background: We never got enough traction to fundraise, but the VC's I talked to really loved the notion of breaking the old Microsoft Outlook time paradigm (which we still use, even in mobile form). I also had a few celebrity-level VCs as users, so there's definitely a pain point there.
Caveat: Since we never got to fundraising, we didn't finish the deck, so prepare for some glaring holes.
NOTE: Let's all assume anything posted here is open for public domain unless otherwise stated