Take Serviette to an event, connect it to a WiFi and everyone there can use IRC/jabber to chat, create a textpad to collaborate on a text (e.g. a meetup protocol), exchange file, maybe even use a PGP/GPG key server to exchange keys at a CryptoParty (simply for testing and not to spread keys on the internet).
Participants can log in to the machine (mosh/ssh), create keys with GPG and use mutt to send mails, both signed and/or encrypted. They can also use the key server to exchange keys, without worrying that the key server will spread it to other key servers. After the CryptoParty, the key server data and emails can be wiped completely. If participants want to keep their keys, they must download them before the cleanup, of course.
Important notice: Keeping those keys should be strongly discouraged, due to the fact that they can't be assured about the safety of the private key material in that context. Rather tell them right ahead that it's a test environment and that they should keep their private key material private and not on systems that others have administrative access to.