So, the question: if the barrier to entry falls to zero for creating web apps, what would you create?

For me, I'd have to say a productivity app. And I don't mean another word processor, address book, or to-do list. I'm thinking of a program that replicates the "Getting Things Done" functionality, that would make it easy to organize your schedule in the same way that GMail makes it easy to organize your email. Sort of a super-Outlook with all the lessons of Web 2.0 built in.

And the first of those lessons is this: produce the appearance of intelligence by drawing correlations from a huge data set. For example, del.icio.us can predict what tags I'll use to describe a link by looking at the tags other people have used and matching that against the tags I've used previously. What if my scheduling software could do the same thing? "Looks like you've scheduled a block of writing time for 9 AM to 12 PM. Based on past records, your writing productivity in that time slot is 52, which is less than your average writing productivity of 78. Reschedule?"

Or better yet: "Other people with your sleep and work schedule report that the most productive times for writing are 7 to 10 PM. That time slot is currently free for 12/18/05. Reschedule?"

"Looks like you've scheduled a block of writing time for 9 AM to 12 PM. Based on past records, your writing productivity in that time slot is 52, which is less than your average writing productivity of 78. Reschedule?"

Nice!

First, I'd make Errorpedia.

Then, I'd make the collaborative screenplay-writing site I've been yapping about for four years. It would begin with one scene. Anyone could contribute a scene at the ending of any other scene. People would be able to easily navigate through all the different forks of the script, save their favorite iterations of the script, generate iterations with preference given to select authors, genres, etc.

(Nod to Glypho, which is collaborative fiction, but definitely not as cool as I imagine it.)

I'd make a personal finance app that helped you save and manage money in context... sort've a simple Quicken meets meets Matt's intelli-calendar (above) on the web.

For example: "Last week you spent $25 on lattes. If you continue this week at the present rate you'll spend $36."

Or: "This month you paid $25 toward your credit card bill. If you continue at this rate it will take you 18 years to pay it off entirely, and you'll end up paying a total of $56,000. Want to tack on another $10? [click here]"

It would be smart, inline financial advice for everybody.

(Oh, and -- I'd inject a little Global Rich List into it, too, to put your wealth in perspective.)