Before this century, most event organizers would use many hours of data collection, tabulation, and payment processing time to prepare for a large (or even a small) event.
If you're looking for more comprehensive solutions for donor management, online customer/parishioner relations management, etc., you may want to tak a look at CRM, Donation Reception, Online Payments.
Nowadays, there is a wide variety of options when it comes to online event planning, registration, coordination, and management. If you want to simply collect data from a certain population, either for a registration or for other purposes, there are many simple ways to do that (some are even built into online content management systems like Drupal and Wordpress).
If you want to dig deeper and allow for much more fine-grained data collection and management of event attendees, or even sell tickets with different levels of discounts and privileges, you can do that pretty easily as well.
This section of the Wiki looks at different options for online registration, forms, and event and ticketing payments.