I created Bandcast for the HackLolla competition. It's using Sencha Touch for the app itself, Twilio (both text and voice), Google charts for QR codes, the Lollapalooza event/venue API for data, Phork for its own API, and Postmark for sending emails.
I want to mention that this is a competition and there's a prize for the most popular app, so I would really appreciate your vote.
The goal of Bandcast is to help you organize your schedule and connect with friends who are at Lollapalooza. I know there's already FourSquare, Facebook, Twitter and text messages for that sort of thing, but this aims to filter out the noise of friends not at the festival. It also makes it really easy to connect with people you meet there without having to give them more personal info like your phone number or Facebook (no more awkward un-friending later).
This was my first Sencha Touch app, and while it's impressive in what it does, there's a big learning curve and I think my time would've been better spent learning how to build a native iOS app. On the plus side it's got the look and feel of a native app (including pull to refresh) and the fact that it's cross platform is awesome. It'll work on iOS 3+, Android 2.1+ and Blackberry 6+ devices, as well as Google Chrome and Safari.
Unfortunately the documentation is pretty poor and out of date, and more often than not when I googled a problem I was having I found the exact same question on their official forums with either no response, or a bunch of "I have this question too" responses. I learned just about everything by picking apart the library itself and from their demos which are all written a little differently. Additionally they seem to be in the middle of switching to a more MVC approach but not all the code is set up for it (eg. the all important TabPanel) so you end up with a bit of a nasty hybrid. It's also slower than a native app, which is unsurprising. But again, it is impressive in what it does. I'd recommend it for a smaller app.
One thing I was really trying to do was make this app work as best as possible when the data network was incredible slow or unresponsive, and for that I wanted to use Local Storage. Sencha Touch has a local storage proxy, but unfortunately there's no easy way to do "load from API, save to local storage, and load from local storage if unable to connect to API". I also wanted to try wrapping everything in PhoneGap but didn't have time before the entry deadline.
This was also my first experience with SASS which is what Sencha Touch uses. Once I figured out how to get everything installed I ended up really liking it and definitely want to explore both SASS and LESS more. I'm way behind on that.
Twilio is my new favorite thing ever. It's incredibly user friendly and very reasonably priced. In Bandcast you can add your phone number and a 4 digit PIN and then you'll get a text message with a verification code. Once you verify your number you can check in to a stage by calling in and following the prompts, or you can have your friends' 10 latest checkins read back to you. The reason for this is because sometimes the data networks get overwhelmed but the voice networks still work. This was really easy to set up and I really want to use Twilio again.
Google's QR codes are also really easy to use. Each user has a unique QR code and when you scan someone else's code you instantly become mutual friends without having to go through the approval process. This is accomplished by setting the value of the QR code to a URL with the user's ID and a unique, unguessable string. Super easy to do when you're at the festival.
And finally there's a public site (which is what I've linked to) so you can get the majority of your friends and schedule set up beforehand. This uses Phork and Phork/it, jQuery and Facebook Connect.
The reason I've been so absent from Forrst is because I've been spending all my free time on this app. I'm looking forward to getting back into things again!