This is a super super simple experiment that creates a chatbox using Dropbox. Just share the folder you cloned it in and run chat.rb.
Read more about it in this blog post.
Ruby and any gems you might not already have on your system. If it complains about a missing gem, run this
gem install [gem name]
Put this somewhere in your Dropbox folder and share the folder with your friends.
After that simply run:
Enter your nickname and start typing :).
ctrl + c
Dropbox will probably create some conflicting copies of 'chat.txt'. Nothing to worry about, you can delete them if you want.