I am setting up a simple email list for temporary use during Meeting of The Minds 2013. In the past we used GroupMe but some people had trouble getting the app to work and there was more handholding to get everyone setup than their should be.
Instead I have creating an email list so that once you are a member and have accepted the invitation you can simply email
90minds@breeze123.com and the email will go out to everyone.
This seems much simpler than trying to have everyone download and learn a separate app for only three or four days use.