Yalla! is an events broadcast system designed to replace the noticeboards found throughout universities. It was written in Rails, and is currently approximately 70% of my school's population has an account. With heavy Google Calendar APIs, anyone can add an event to Yalla! just by sharing an event to the website's email address. Other uses can then view all events, and add / cancel RSVPs. Events users attend are automatically added to their personal calendars, and changes are synchronized across everyone's calendars. Hosts can track their attendees and contact them in one click.
Because of privacy, the web app is password protected. If you're interested in seeing Yalla! in action, just get in contact with me, and I can generate a passthrough key
The current iteration is found here: yalla.nyuad.org