Conference registration for a cooperative of thousands of libraries.
OCLC is the cooperative that libraries around the world depend on to catalogue and share what they hold. We built the system its members use to register for conferences and events, on Drupal.

The problem
Registration is where a conference either runs smoothly or turns into a spreadsheet and a long email thread. A cooperative makes it harder: attendees are member institutions rather than individuals, sessions have capacity, and pricing depends on who is asking. Doing that by hand does not scale past one event.
What we built
We built conference and event registration into their Drupal platform, so an event and the page describing it are the same thing rather than two systems kept in sync by a person. Members register, choose sessions and pay through it, and the staff running the event can see who is coming without exporting anything.
What it did
An event registration platform we built on Drupal, used for events attended by libraries in dozens of countries. We built it and we still maintain it.
Tell us what is not working. You get a straight answer about whether it is worth doing, from the people who would do it.