Ask HN: Is there a back-end HTML form processing service?

Is there a service that can handle all the back-end stuff of HTML forms? Like Wufoo without the front-end HTML/CSS/Javascript.

The reason I'm asking is because I recently made a conference sign up form using Wufoo but I couldn't customize the form as much as I'd like to. I wanted to have the form prevent users from selecting an event that has already had a certain amount of people sign up.

Does anyone else here feel the need for a service like this? Or would you prefer to create the back-end from scratch? I was going to but I only had a few hours to create it.