Platform
To create a code: IE 9+, Firefox 3+, Chrome 3+, Safari 3+
To view a code: iPhone with Barcode Scanners that opens in Safari. Other phones/methods coming soon. Android does not support opening .ics files.
Steps
Task 1: Make a code
Go to http://rscanvp.com
and click "Get Started". try filling out the form (it does not save your data). Try creating a code. (It does not save your settings as you more back and forward yet). Download the code (not implemented). Inset the code into your favorite graphic design program (ie Illustrator, Publisher).
Task 2: Scan a code
Scan the QR code in the following poster (need link). The URL goes to http://rscanvp.com/view.php The sample ICS file is open-able in iPhone Safari (but not a web view in a different app), as well as on Windows with Outlook installed. (The Add to Google Calendar and set up email reminders is not implemented)
Task 3: View RSVPs
Go to http://rscanvp.com/admin.php. See (fake) RSVP counts. Can edit event details and code (fake data is filled in)