I want to create online forms similar to Wufoo, but with the ability for people to save their work and return to it -- and also for multiple forms to be linked together. I'm not technical, and I don't want to hire a programmer to create a system which I cannot change myself. Seems like there ought to be something that's one level up from Wufoo in sophistication, but not so technical that it would require specialized knowledge.
I would recommend you look at Gravity Forms which you can use on a Wordpress framework. The forms are easy to put together, and have a great deal of flexibility and options for integration with other platforms. You can easily use Gravity Forms for multiple stage forms.
JotForm.com is GREAT! I've been using it for years and it keeps getting better. The whole thing is drag and drop and you simply add a line of code in a wordpress page or post or other site and the form appears. When you change the form it updates on your site. I use it all the time.
I've tried LOTS of options, but never had one work so well. It's one of the few services that simply works the way it is supposed to so I keep using it.
Also, Zapier (which I haven't used as much) links your forms to other places you need data.
Here are some sample jotforms:
The best way is to rely on an easy-to-use online tool that walks you through the entire process. The site should take the guesswork out of the whole thing. I'd suggest using http://www.fieldboom.com/ to create advanced forms because it does all of those things. You can even try it out for free to see if it meets your needs. And if you ever decide to do a survey, it can help you with that too.